Rather nice analysis.
I think somewhere along the line they over simplified the textures, perhaps for performance reasons. I have seen comparison videos of some cut scenes that were much better looking from a year or two ago that have lost so much in the final version. That may have been what happened.
Or perhaps, with the ME1 Turian, they relied more heavily on the art (or skin) that was wrapped around a more basic model to give the character life, where as with more advanced computing power, they felt an actual more detailed model would provide those shadows and visual interest that raw artwork had a decade ago.
Think of it like TOS Klingons vs TNG Klingons if it helps you sleep better 🙂
Game engine/model changes aside, the bright lighting on the Nexus doesn't do the Turian faces any favours since it washes out a lot of the detail. They look more like their earlier incarnations elsewhere when the shadowing gives them a bit more depth.
