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.
The trouble with OS2 is that there's a "winning strategy" behind many if not all of the battles. If you've figured out what it is, whether by luck or judgement, you'll walk it. If you haven't, you won't. Arbitrarily hobbling the ability to succeed based on the experience of the former is unlikely to do anything usefully interesting but it will likely make it impossible for people who haven't studied every strategy and actually puts them at a disadvantage compared to those who went before: so it really only becomes hard for new players, who will probably give up and tell all their mates, "this game sucks".
Some have suggested imposing your own limitations to increase the challenge. Even as about as non-hardcore a player as you can get, I have often done this myself so I don't buy the claim that it's unrealistic, and for those who need hand-holding in order to set themselves a challenge, I'm not sure there's really an answer to that.
