That's a problematic mechanic for this type of game, rk47, because giving a bad player less xp means that they are basically just screwed. Enemies don't respawn in DOS and being underleveled can be hugely debilitating.
Batman Arkham City actually did something that worked well, in this regard. The more skillfully you fought, the more xp you would get. If you never broke your combo, never got hit, and used a wide variety of moves, you would get more xp.
But unlike DOS, leveling up in Batman didn't necessarily make the game easier. Enemies would scale to your level, so leveling up means you fight tougher enemies, many of which have built in counters to your easy techniques. However it also means you can unlock new abilities.
I feel that is the correct way to do things. When the player does a good job, reward them. Don't reward them by making the game easier, reward them by making it more interesting. New options, new enemy types, more varied gameplay. If they are struggling, then slow down how quickly you introduce new mechanics. Clearly they haven't gotten the hang of what they're currently dealing with.
