I honestly have no clue where you're going with half the stuff on here.
Yes, we do know they planned a trilogy. Because they said they planned a trilogy. We can't trust that statement because... Marketing?
I can absolutely call on the sequels for my conclusions, because the first game specifically didn't give all the answers. It introduced the setting, and at the end it got the plot rolling. They didn't need to cram everything in one game because they were planning more. I knew this before I finished the game.
You say they had no plan. That is baseless assumption without proof. Don't invent "facts" to support your narrative.
How did 2 diverge? 1 set the scene, introduced the setting, and set the stage for the conflict. 2 progressed the story, introduced new details, and continued leading towards the conflict. 3 gave us the main conflict. It's called "overarching plot".
To your bold text: as a (hopeful) author I can tell you they almost definitely had at least an outline done of the next two games as they were writing the first. They may not have had full scripts, but I'd bet my last dollar they had the events they wanted shown penned out. It's just how you do things when you write. You plan out events in future installments so you can leave hints in previous installments, which is what they did. You continue making baseless assumptions without proof and present them as facts.
Lol this actually made me laugh. I never said they didn't need the relay network........ For instantaneous travel. And yeah, there is both an in-universe and out-of-universe explanation for why the Reapers can fly right in. You read for it? It's because they are gigantic super-advanced space ships and there is literally nothing between the edges of our galaxy and dark space. There's nothing for them to "enter" because there is no divider. I honestly can't think of a metephor to explain it that's simpler than just saying it. They can enter our galaxy because there is nothing physically stopping them from doing so. They are ships that can travel at FTL speeds. That's it. They don't need to be gods to do it. The Arks went into dark space without a relay. They entered Heleus without a relay. The Reapers were just outside our galaxy, and it still took them three years flying at FTL to get here. How does that make them gods?
And the reason Sovereign was taken out in Mass Effect 1 is because of two reasons (both explained in game). 1: it was an entire fleet of dreadnoughts hammering it with kilometer long guns. 2: It had transferred it's consciousness into the dead Saren to kill Shepard and activate the Citadel. When Shepard killed Reaper Saren it caused feedback which caused Sovereigns kinetic barriers to falter and it temporarily lost function. The Reapers aren't protrayed as gods in Mass Effect 3 either. There are constant reports of fleets taking out Reapers, just with heavy casualties, which also happened when Sovereign attacked the Citadel. It slaughtered countless ships before Shepard killed Saren.
Yeah, there was an in-universe reason why they didn't capture the Citadel right away in ME3: there were a tooon of ships around it. It took a huge push for the Reapers to finally capture the Citadel. It's seriously explained in the game. Did you read the emails and/or listen to the conversations?
Lol what lore from the first game??? We barely even found out WHAT a Reaper even was in the first game. There was barely any lore there, and what little there was was most definitely not discarded. We learned the Reapers were a thing. They lived in dark space. They plan huge purges of the galaxy. They are giant ships. What else was there in the first game???
Point Two: You realize the Citadel races DO control the relays, right? They know how to activate them, they know how to deactivate them. Again, that is explained in game. The First Contact War happened because humans (who hadn't met any other alien race yet) were activating relays left and right. So, a race that had had no contact with any other sentient life managed to figure out how to turn on and operate these relays. The Turians found them doing this, boom, war. Again, look it up. First Contact War. It's actually forbidden to activate a relay without first locating it's twin. The reason for this is because the Asari activated a relay without knowing where it went, and were suddenly up to their eyes in rachni. This is all history that is readily available in game. So, if we dumb hairless monkeys can figure out how to turn them on, then I think it's safe to say that the Collectors can fiddle with the Omega-4 relay. Considering, ya know, they work for the machines that built the relays in the first place. I think Reapers know how to use Reaper tech. Stop twisting facts. :p
Part Three: sigh Seriously? I don't even want to fight you on that. Bravo dude, it took serious skill to misinterpret what I was saying. No wonder you couldn't follow the games.
Actually read my comments, or I won't be able to treat this with the already tenuous level of seriousness I'm already managing.