I think that reducing experience gained after level ~10ish would make the game harder and, in my opinion, more fun by default.
For me this would do the exact opposite. I tend to view role-playing games as predominantly about role-playing,
not combat. I'm not really interested in "hard" and neither am I interested in analysing the minutiae of builds and the ideal tactics. As far as I'm concerned they're obstacles to be overcome and not the point of the game: the point of the game for me is to be who I'm playing, to explore, to learn about the other characters, to absorb the story and atmosphere. Combat trails rather a long way behind all of those.