If we can learn anything from ME2, it's that people value anecdotes more than anything else. Both ME1 and ME3 do so many more things in a superior manner, but, because ME2 had nice moments with side characters (yes, the majority of your crew are side characters), people regard it as the best game in the trilogy, despite all the absurdities the game provides. The value of anecdotes is so high, that even the flaws were turned into memes that work for the popularity of the game rather than against it.
Firstly, anything that does not move the main plot forward is a side element, be it a side quest, side mission or side character. Taking ME2 as an example, the plot is stopping the collectors from abducting humans. Whatever action you take that improves survival rates of your crew or whatever are nice to haves, but not relevant in terms of plot.
That would mean that Mordin is a main plot character, because without him, it wouldn't be possible to be invisible to the swarms, and Horizon wouldn't happen. He was vital to the progression of the story. His loyalty mission is a side quest though, just like all loyalty missions.
Miranda would be a main plot character since she brought you back I guess, but technically it wasn't required for her to be a squad mate. Still, she's a main character.
Jacob is an introduction to Cerberus, nothing Miranda wouldn't be able to do, so, he's currently a plot character technically, but an unnecessary one and functions more as a side character.
Garrus is a side character.
Grunt is a side character.
Jack is a side character.
Samara is a side character.
Tali is a side character.
Thane is a side character.
Legion is a side character.
All DLC characters are side characters.
EDI is more important than the majority of your squad mates... And so is TIM.
People love to say that the ME1 characters were bland and shallow, but they had a clear purpose to the main plot.
Ashley/Kaiden serve as the trigger for getting the vision from the beacon.
Tali serves as evidence to show Saren is guilty and to allow you to pursue him.
Liara serves as an expert on the Protheans to help you decipher and interpret the visions from the beacons.
Garrus, even though he doesn't forward the plot, functions as the embodiment of frustration towards the council and C-sec regarding the Saren investigation, i.e. frustration towards stagnation of the plot.
Wrex is arguably the only one without a clear influence on the plot, other than the conflict on Virmire, where his role of supporting you temporarily turns into stagnating you. And funnily enough, he's considered the deepest one in ME1. Because the anecdotal experience with Wrex is a lot more valuable than the actual real value of forwarding the main plot that the other characters provided. Funny how that works.
I still maintain the perspective that the downward spiral of Mass Effect started with ME2. It got accelerated because of the high praise despite the many flaws in many areas that did not and still do not receive criticism. The downfall of Andromeda in particular was trying to structure the game as ME2, making it more open and fail to deliver high quality characters. There was no delivery of the necessary anecdotes for people to value the experience, and this time, the memes worked against the game rather than for it.
The infinite praise of the flawed game that is ME2 needs to die already. Let's start praising something else, like, this;
www.usgamer.net/articles/mass-effect-3-deserves-to-be-remembered-for-more-than-its-ending
