I find this to be an invalid comparison.
Your argument runs
If a dev puts effort into making a 2d game look good, then it will look better than a 3d game with no effort put it.
A valid comparison would be to see which looks better out of
A shit 2d game and a shit 3d game
as well as a good 2d game and a good 3d game.
3d will win in both cases