The inflection point for diminishing returns appears to be the PS3/360 generation

[kupomogli]

When comparing jumps in visual from current to next gen.  We only have end of gen and beginning of gen to go on so to make it fair, you need to compare end of gen sixth gen to seventh gen.  Games get far better looking later in the gen than the beginning of the gen.

Morrowind

Oblivion

Witcher 3