It is just you (and whoever agrees with you, I guess). If it wasn't for the presence of the shoe-horned mindfart that are Asari I'd say the Quarians were the alien species originally designed to be most like humans. Alas, 15 year old boys need their titillation, so...
They have nowhere near a "distinctly insectoid body structure" and I can't possibly see how someone with a pair of functioning, healty eyes can ever say such by looking at them. And mind you, I'm saying this as a person afflicted with very high levels of visual myopia who's worn spectacles 24/7 since the age of 7. I cannot cross a road safely without my glasses, that's how bad my eyesight is and I'm still slack-jawked amazed at the word "insectoid" being used as a qualifier for Quarian morphology.
Hmmm...maybe it is a problem of thought process, or scientific ignorance rather than a visual limitation; but I ain't touching those.
Either way, no. The Quarians are not morphologically insectoid in any manner. They are cleary and visibly bisymmetric erect humanoids with digitrigade legs and three fingers per limb. Their stance is not even that different from real-life double leg aumputee athletes who run using those lightweight steel prostetics.
I'd bet they (and the Turians) all things being equal can jump higher from a standing position and sprint faster than an equivalent human; i'd also bet they can't throw a good kick to save their lives compared to a human.
You mean Dextro amino-acids? Because I don't remember anything about "fluids", that is a state of matter, amino-acids are organic chemical compounds that can be found in different states of matter.
Anyway, those are no more exotic than a different baseline body Ph or the fact Terran house cats aren't affected by LSD and HUmans can, or a rabbit's ability to digest celulose while we lack it. It is also no indication whatsoever they are space bugs under those suits.
Not that I have a problem with space bugs, or the quarians being lizards or whatever. I'm just not followign the logic here and what is presented as evidence for the train of thought. Especially when dextro amino-acids are present on Earth and we eat them without dropping over dead on the spot, unlike what ME science fail about it seems to suggest. So if Quarians are dextr-based and that is something that exists naturally on Terra, how can can this possibiliy be put foward as evidence that they should not be human-like?
First, as someone who romanced Tali on my first playthrough and was caught unaware that romacing an alien was even an option when I picked the game up, I must say I chose to be slightly offended at that comment. It is not the fault of players who got enamoured by Tali's personality, character and her "I don't need to show my t*ts" femininity that BioWare decided to take a ****** upon the franchise and use a (badly) photoshoped stock picture of Miss Britain or whatever to turn our mystery lover into a bad joke and make her look like a freak.
Second, even before Tali was a romancable option in ME1 through her helmet we could already see a very humanoid-like (and definitively non-insectoid) head with proportions and eyes and nose similar, if not equal, to humans. So that derrails your conspiracy theory that you didn't get space bug Quarrians (what? the Rachni and Tresher Naws weren't enough for you?) because Tail had to be romancable.
As I said before, the Quarians are the most human-like race out there apart from the (ugh!) obligatory Asari "sex sells!" mindfart catering to juveline hormones and ME1 shows us they were that from the beginning. If the original concept on paper back at the design studio envision them as chitinous space bugs I can find zero evidence even hitning at it in the 3 games and multiple dozens of hours I put into them. If you have such evidence please show it to us, I would like to see it. That concept might even a better one than what we got, who knows? Well, no one unless such evidence is presented, right?
I don't accept opinions of the youngest, least experienced, most immature and most ignorant companion NPC in the entire setting as an argument for anything about ME.
I don't trust information via implants from a megomaniacal Krogan scientist either.
In fact, I don't trust Krogan at all. 
And what does "though" mean? We beat the Turians at their own game in the First Contact War, does that makes humans "even-more-though"? If its refering to military prowess than the Turians being good at it is due to superior tech, training, tradition, experience and a militaristic culture. I see no indication in the game that the average individual Turian is a badass or innately a mighty individual warrior, unlike the Krogan or Yagh who are powerhouses out of sheer racial bulk and strenght.
And how does a race that has been exterminated in the billions by their own toasters and who can die if you sneeze on them merit such a qualifier to begin with? Was Grunt high or something? I'd understand if he meant they are still around even with all the crap that they've endured but "though" is hardly the word I'd use, "preserverant" or "survivors" maybe. By the Quarians own admission in ME3 they are very crappy ground trops. Yeah, grunt is full of it.
How so? Turians are chitinous because their skins have evolved to hold minerals and be carapace-like to protect against high solar radiation due to a weak planetary magnetic field. Quarians come from a world with an older, weaker sun than Sol. If the the Quarian home system star is practically the best direct opposite in the entire setting of the evolutionary imperative that gave Turians their chitinous look, how can this ever be used as evidence that Quarians were "originally supposed" to be more chitinous?
Again, "originally supposed" presumes access to evidence from the designing team or knowledge about such evidence. Could you point us out to it? And again, It may well be the Quarians were originally envisioned by the developers of ME as humanoid bugs, but there is no trace or indication of such in the finalized setting as it was presented to us.
I see nothing chitinous or inset-like about the morphology of the Geth, except in Colossus which looks nothing like a Quarian. Speaking of alternate Geth designs the ME1 Leapers sure do look mamallian, even simian, in design to me.
Regardless, using Geth to back up yuour claim is the equivalent of an alien race saying Humans must be box-like humanoids with clamps for hands when they see our 1950's era robots.
Its just you, really. You have not mentioned a single "established fact" about them, only your misinterpretations of what the games show and unsupported suppositions.
Yes, I find it odd a fellow ME player managed to ignore most of what the game tells us about the Quarians, takes his/her unfounded suppositions for facts and asks a silly question, while casting blanket asperisions at people who like Quarians as they are enough to roleplay their Shepard having an emotional and sexual relationship with one.
Quite odd.
I'm going to concede here and confess I am not Codex or WIki reader. I look at my ME trough what it showed me, not through what someone else wrote about it. That said I don't remember hearing anything about "fluids", "carapaces" or "extra fluid" in any sentence relating to Quarians. The *only* similarity between the two races that keeps being brought up is their dextro amino-acids.
The 3 fingers per limb and being digitigrade don't even count because most other non-Asari, non-totally-alien races are like that. The Salarians aren't Dextros but they still have 3 fingers and digitrigade legs, the Vorcha are also digitigrade. The reason? Designer laziness and saving time/money/effort with animators. there is no special meaning to any of it...sadly.
Heck, even the amonia-breathing (amonia-gasping?) Volus have 3 digits. Does this mean we can use it a evidence pointing that Quarians were "originally designed" to be a non-oxygen breathing race?
All this said...
Do I think the Quarians look anything piece of crap photoshoped human picture that Tali gives you? Heck No!
In my head, Tali didn't even had hair. I wonder how that glorious mane on the photoshopped pic managed to fit under her helmet? Or how we never saw strands of it through the visor?
I'd also bet the quarians are...pale, probably albino-like, whether they be mammalian, reptilian, bug-like or whatever else. A lifetime in suits without natural sunlight doesn't exactly promote a nice tan.
EDIT:
This is what I guess for responding to the OP without checking the rest of the thread. I missed the posted art. 
About the "character concept" pic, the first one; assuming it is a legit document issuing from thr design team it settles the question that the Quarians are very much human-like, and were envisioned as such from early design stages, meaning the matter is settled. No space bug or reptilian Quarians. It also means my assertion that the Quarians are the most human-like aliens in ME (apart from Asari, which are just there for fanservice and Mary Sue purposes so they don't count).
That pic actually looks very similar to what I evsisioned Tali to look like under her helmet when I was playing the game. No hair, albino-like, very human but with an "uncanny valley" disturbing vibe about her. I think the face onm that is to chubby and round from what we can see through the helmet and the eyes are likewise excessively angled. I don't know why they are black and turian-like when they are shown to glow trough the helmet. She also looks younger than I expected, a bit too child-like.
Apart from that, it is a very good design. While it does look disturbingly alien, it is still the face of a sentient creature my Paragorn Shepard would love and set out to build a future and family with.
Too bad the games couldn't give us romanceable Human females that could hold a candle to the characterization and pathos of Tali, or didn't look like sluts.