So, now it seems, like you're upset about there being a lack of pure filler in ME3. You could do the N7 missions as they came up... or you could wait to do all of them near the end of the game (there were some consequences). You could do both Attican Traverse and Turian Platoon/Turian Bomb after doing Rannoch (again, there were consequences). The game did make you aware of things in such a way that one would perhaps naturally follow the suggested story line... but there were ways that you could do those missions in different orders... and unlike ME1, if you did juggle the order, it resulted in consequences that affected the main story line (apparently causing you to believe that they were part of the critical story rather than the optional side missions they actually were).
I needed the war assets. I remember now. Not doing those missions just seemed dumb. Since I wasn't going to play any MP, I needed to complete those in order to get the war assets I needed.
ME1 actually gave you very little room to juggle the main storyline and, where you could, it had so little consequence to the main story that it was really not worth bothering about. You could, for example, do Therum, Feros and Noveria in any order... but did it really make any difference at all to the story or how the NPCs responded to Shepard's character? No. You could do Therum after Virmire, which did change Liara's reaction to being rescued - a very little bit... and that was about the extent of it.
I don't really like the distinction between the critical path and side quests. ME1 gave us all those Uncharted Worlds to explore in whatever order we wanted and for whatever reason we could imagine.
ME2 offered nothing of the sort. ME3 offered some, but again, the need to acquire war assets forced our hand somewhat.
If, however, it had worked like Power in DAI, where there was vastly more available than we needed, then we could have done them or not done them as we saw fit.
I also don't understand how the war assets in ME3 make any sense with regard to the ending.
A fully Renegade Shepard could save the council just as easily as Paragon Shepard and both successfully took down Saren in virtually the same way... no matter what they did prior in the game.
That's a definite plus. Being constrained in our choices later because of what we did earlier limits our possible character designs.
Maintaining the coherence of the protagonist's personality is the player's job. The developers need to stay out of the way and let us do that. Since they cannot know what motives we used to justify previous choices, they can't know what future choices are compatible with that.