Problems with the 3D perspective start to appear when you play Competitive matches against strong opponents. It's incredibly annoying when you make wrong clicks or simply don't notice chests, artifacts, etc., just because the camera angle wasn't right. Because of these small things and their consequences, the outcome of the game changes significantly.
And I still tend to think that the graphics in the game are far from the most important thing (specifically the graphics, not the style). The graphics engine is a matter of habit. I have quite a few complaints about the fifth game, but they relate directly to the gameplay, and the graphical interface is a secondary concern.