Sovergin played it stealthy because a single Reaper couldn't stand up to the combined forces of the Galaxy. When Sovereign was gone they went with plan B. Use the collectors to harvest humans to create a new Reaper to replace the destroyed one. When that one failed they said **** it time to attack. Destruction of the Alpha Relay delayed them but that 6th month period they spend at least a good 2 months taking apart the Batarians to provide the front line troops needed to assault the various planets. Hence why the first level only has Cannibals as enemies. With the other troops showing up as the Reaper's spread to other species colonies.
Ok, let´s go though it. I am aware why Sovereign did what he did in ME 1, thx for explaining it once again. I am fine with the explanation if ME 2 and 3 didn´t open a lot of questions about this chain of events and that was the actual point.
ME 2: The Reapers already had troops there in form of the Collectors. Ok let´s explain that away with Collector ships suck, you can blow one up with a frigate (and the Normandy doesn´t need any upgrades to do it).
ME 2: Harbinger is able to control his slaves in real time from Dark Space. That´s nice, so it shouldn´t be a problem for Sovereign to tell his buddies in dark space, that there is a change of plans. Even if he, for some asinine reason, doesn´t have the capability to call home, the Collectors have. He would have to pass through the Omega system but uh well, the Collectors are able to come and go as they please and even if Aria´s goons spotted him, they had no context to make sense out of it. Let´s not talk about that it would be prudent to equip Sovereign with some QEC capabilities to call the Collectors at least.
ME 2: So the Collectors/Reapers plan was to build a human Reaper. Sounds well ok. What´s this thing supposed to do then? Call the heretics and get his arse kicked like Sovereign at the Citadel?
ME2: So the Collectors plan was to build a human Reaper. Oh that´s nice. Where do you get the building materials? Seems you need the vast majority of a species to build one. Fun fact, 90 to 97% of all humans still live on Earth. Ok let´s attack Earth! Hm nice try, you only have to pass Arcturus station and several fleets to go to Earth and then face another fleet there and planetary defenses. And well Collector ships suck. The fleet at Arcturus and Earth may not have Shepard´s tactical genius(lol), Joker´s leet piloting skills and their frigates may not be so advanced as the SR-2 but there are a lot more frigates...and cruisers and oh dreadnaughts and let´s not forget the carriers and fighters. And well, I somehow doubt that Arcturus station is an umarmed sitting duck. As far as we know the Collectors had ehm 2 ships?
Even if they miraculously bypassed all that, these things are sitting ducks on the ground. the cruiser was forced to lift off after getting shot at by 4 hastily installed GARDIAN lasers. I somehow doubt Earth is so sloppily defended. Air defence controls tend to sit in bunkers and the mechanix on Horizon was able to evade the Seekers by sitting in an closed room.
So the chances of actually completing the human Reaper are close to zero unless ME 3 is wrong and a few million are enough. In that case, why build only one Reaper of each species? There are possible explanations but seems no one cared at BW.
ME 2: Legion describes that Sovereign had been searching for allies for over a millennium in order to bring about the cycle once more. Eh ok. Lemme see. Cycle delayed for over a millenium is preferable to just turn on the engines, fly for six months and use another relay? AIs could have overrun the galaxy in one millenium. Ok let´s put it into the "Nazara just pulled the geth´s leg for some reason."
ME 2 Arrival: Oh there is another door into the galaxy. It´s in a backwater system and can be activated from the other side. Let´s just take this one instead. "Hi, here´s Sovereign, there are big problems with the usual plan, let´s take the Alpha relay." It´s not as elegant as popping up at the Citadel but will have to do as a backup plan. At least it´s more subtle than flying around for decades finding useful pawns.
ME 3: Six months later. Oh really? So the guys hanging out in dark space for 50k years were too lazy to spend six months of their time? But they were happy waiting a few decades until Sovereign figured something out, and their backup plan was "let´s wait until the Collectors have build a Reaper. No idea what the youngling is supposed to do then. He starts from scratch after all, but Harby thinks humans are so special."
ME 3: ME 1 said that the Reapers assault the Citadel every cycle to gather info and shut down the relay network. Oh that sounds sensible, perhaps we should attack the Citadel before Earth to minimize resistance. Ah no, that would make sense." Hm perhaps the Reapers were unable to assault a fully prepared Citadel? Ah no, they just take it off screen while you are busy playing with Cerberus.
ME 3: I am the Catalyst, the Citadel is my home, the Citadel is part of me. Oh really? Where have you been when Sovereign dry humped the tower, trying to call your buddies? Don´t the Keepers still listen to the Citadel and it´s a part of you? What are the Keepers needed for when the Citadel Master Control is part of you or at least you are sitting on the "hard drive" next to it?
There are some explanations but Shepard didn´t bother asking. Oh come on, it would be only a few lines of dialogue and the coding to grab flags for stuff accomplished in ME 1 is already there, if you don´t want to confuse new players. The game knew it if you had a license from Elkoss Combine in ME 1. So if the game wasn´t a save import, don´t offer the dialogue option, like the one about the Leviathans unavailable if you didn´t play the DLC.
In game it´s a legitimate concern: "How can the Citadel be part of the Reaper intelligence when they needed Sovereign to open the door?" But yeah, who cares. Out of game: Hi, we are BW. We just opened a giant question mark about the whole plot of ME 1, but who cares? We don´t, we didn´t even bother to put in even a flimsy explanation that would stand up to a cursory glance. the explanation: The protheans did it would be an unbelievable miracle but at least an acknowledgement.
It´s not about, that it´s totally unexplainable, this is about not bothering at all about the story of a third of the trilogy. You can´t keep 100% consistency and remember everything what happened but that was the central plot in ME 1, not some minor thing like ME 2 automatically assuming that you were mean to Conrad Verner in ME1 .
READ THE FOLLOWING CAREFULLY!
I am aware that it´s impossible to craft a consistent world without some hiccups.
I am aware that the game can´t explain everything in fine detail.
I am aware that you can nitpick a lot in nearly every franchise, if you want to.
I am willing to give the benefit of the doubt to some stuff or at least gloss over it.
But!
There is a limit to my willingness to suspend disbelief. We aren´t nitpicking anymore, this is on the level of "Hi we are Bioware and we don´t give a f*ck about ME 1´s plot."
So about this chain of plans. This is an unbelievably dumb chain of plans.
Plan A: Open the Citadel Relay.
Plan A "Sovereigns version": Spend a long time, risking exposure, finding allies then assault the Citadel.
Plan B: Activate the Collectors to build another Reaper.
Plan B 1: Start from scratch where Sovereign failed.
Plan C: Activate the Alpha Relay, kill everyone.
Plan D: Fly for six months or 4 +2 harvesting the batarians and then kill everyone.
Plan "We are so unbelievably stupid, the average IQ of the galaxy drops to zero as soon as we enter": Hide your central AI on the Citadel without any means to open the relay itself or in case it had that ability; prevent tampering or at least call Nazara and let him know that some pesky four eyes are meddling around in the Citadel. Could you please eat them and then reset to factory settings? it´s not likely any other species is able to show up in the next uh 20k+ years at least.
A more prudent plan would be:
A: Open the Citadel relay.
Part of A: Make a call to the Citadel and check in with the catalyst if everything is ok. In case of no or negative answer, go there and fix it.
B: In case that the Citadel relay is unavailable, switch to Alpha Relay, then capture the Citadel.
C: In case this doesn´t work, too, just fly for 6 months, enter the galaxy, then capture the Citadel.
D: Harvest everyone.