I'll be honest and state that I really don't see much of a use for the Quarians, nor do I see a utility for them that can't be met by the Geth.
The Geth have as much logistical capability as the Quarians, and they are significantly less vulnerable (and flying in much more stable craft).
Post-upgrade, you really have no way to say whether the Geth are incapable or not of independent and innovative capability.
You have your right to an opinion, but it isn't supported by the lore or else the quarians wouldn't even be a factor in the war planning in the first place. The original purpose given by Hackett for going beyond the Veil in the first place has nothing to do with needing the geth.
They don't, at least not in terms of intergrating with the forces you already have. Geth ships have no life support, for one, so are completely unusable on a large scale by other forces for anything except cargo transport, which they probably aren't designed for anyway. When one of the major stated logistical problems is actually getting the shipless krogan to the battlefronts, the quarians have a definite edge in the lore right there.
I don't, but neither do you. I am merely making an extrapolation based on what the two "Species" (I use this term loosely and for the sake of brevity, because software programs aren't a species, but that isn't what we're arguing), have proven capable of by themselves. We don't know the nature of the Reaper technologies given to the geth or exactly what they do other than an upgrade in processing power, nor do we know if the quarians couldn't benefit similarly from other Reaper technlogies. It is all supposition
You're not highlighting any particular advantage the Quarians have over the Geth. You're stating a characteristic that the Quarians have and implying that the Geth do not have it, but I'm failing to see the basis for where this is the case.
I think you're also mis-stating the value of the Geth. They're a lot more than 'meat for the grinder', especially when compared to the extremely fragile nature of the Quarians in comparison (both in space and planetary combat). You have mechanized, intelligent platforms capable of deploying in hostile environments with maximum efficiency that not even the Krogan or Turians can jump into. Said intelligent platforms are capable of self-repair, and are rather durable. They're also capable of processing information and communicating with each other at light-speed, and capable of coordinating on a level that no organic can match.
As for culture, I do indeed throw aside the Quarian culture for the Geth. Because, to repeat sentiments, I question the nature and veracity of your statements about the Quarians achievements, especially in the face of the boon that is possible from what the Geth can offer post-upgrade. And you're failing to account the Quarians own insulated culture, compared to the Geth's rather practical approach to isolationism: They don't believe that anyone will accept them, and they do have history and experience to back them up.
because we know the quarians have these characteristics, whereas we have no ideas as to the capabilities of the Reaper upgraded geth. It's shaky either way, but I'm making conclusions based on the (admittedly limited) evidence presented, circumstantial and otherwise. The fact that a mere 17 million quarians could in any way challenge billions of geth more than proves that they have advantages in terms of innovation and efficient resource utilization, and do not lack for utility.
Similarly, I think you are mis-stating the value of the quarians and overstating that of the geth. On an individual platform basis, from what we've seen the geth seem to be woefully incompetent in combat and reliant on raw numbers rather than any tactical or technologial advantages (our small squad kills thousands of them over the course of the game, and other engagements in which we witness them are usually hundreds or thousands of platforms vs a small number of organics ala Haestrom). I'm not questioning their ability to marshal enough material to be highly useful, but it is in the same way that the USSR was useful in the Second World War. If you have the krogan, you already have an essentially limitless pool of shock troops to perform the same function. The fleets are roughly even, with the quarian ones being more varied and technologically advanced while the geth fleet is more suited to sustained conventional combat. What then do the geth offer that no one else can? I won't restate what the quarians offer, because one could reread my last post, but suffice it to say I think their relative strengths are more useful considering the asymmetric nature of the conflict and other forces at your disposal, and their contribution via the only system we have is objectively higher than the geth. The numerical size of one's army and resources isn't the only means of measuring a civilization, or the Soviet Union would have easily won the Cold War. That's a limited viewpoint. Do you think the contributions of Cerberus to the war effort are useless because the Alliance has billions more meatbags and thousands more ships to throw at the Reapers, who we know can't be beaten by any conventional means anyway?
Again, I am arguing what is and has been shown to be true and extrapolating a conclusion I think reasonable, you are arguing what is possible based on something that we cannot verify due to limited extrapolation on the nature of the upgraded geth, apart from some vauge "alive" Pinocchio nonsense. Also, how is the geth's isolationism more practical than that of the quarians? The former calculated that they would not be accepted and thus chose isolationism based on prevailing organic attitudes towards synthetic "lifeforms". The latter was ejected from the galactic community against their own wishes, and continues to face disdain and racism 300 years later, stymieing any hopes of intergration. What else are they supposed to do than isolate themselves? Both have logical reasons for their decisions.
As for the Geth's capabilities compared to the response of the Quarians during the opening stage of the war, it's explicitly stated that the Quarians have a specialized EMP device that is capable of blocking and disrupting Geth programming.
To counter your Finland/WW3 statement, it would be more akin to the Fins going into each country and releasing a very potent, very virulent airborne disease that utterly debilitates and destroys the entire population of each country. And you're leaving out the element of surprise, where the Geth are focusing their resources elsewhere (like preparing their fleets and armies for war against the Reapers).
I think you're also aggrandizing a theory for the future of the Quarians and the Geth.
Again, the quarians brought a technology that they themselves created and the geth could not counter or adapt to in sufficient time. It's no different than Israel winning so many wars against superior foes via applying their limited resources in a more efficient manner, or the British putting down the Bambatha Rebellion through superior technology alone despite massive numerical disadvantage.
If those societies could not use their vastly superior resources counter said disease, it is either the Finns being technologically innovative or the rest of the world being incompetent in chemcial/biological warfare. Technological superiority is an element of warfare, and I would argue the most important one everything else considered. It is no different than bringing previously unknown gunpowder or atomic weaponry to other conflicts. Element of surprise should only go so far when you are outnumbered more than 1000:1. The fact that the geth could not adapt by themselves despite utterly massive material advantages points to an inflexible society that is extremely lacking in adaptation or innovation. The fact that the quarians could develop such things lends evidence to the argument that they would be more useful in finding unconventional solutions to combat the Reapers.
Bluntly put, but not incorrect. This is all theorycrafting and I haven't claimed otherwise. I'm stating my opinion, as are you. The fact is that the relative strengths of the two are objectively equal according to the system of measurement used. I'm not using the potential of Reaper technology, because I don't know how much the quarians could be improved by harnessing it, but I do know other organics are capable of such.