I've already spoke on how you are role-playing incorrectly, here's how the mechanics support the idea of role-play being how you would explore the dungeon.
You know what has exactly the same chance to hit as a fifth level fighter (needing 16,000 experience)?
A first level wizard with a +3 sword.
What's important is the play of the game. The differences between most characters between levels 1-9 are minimal. A few extra hit points for some. But there is a good chance, for most classes that when you level nothing may change.
But does it matter?
Not in the least. You determine your status as a winner by surviving and surveying the pile of gold you've accumulated. You enjoy the play of making decisions and attempting to survive.
I'll let you in on a secret - the 'talents' and 'skills' I let my players have is illusionary. The design space that they are designed to fill, would not need to be filled if they didn't take the 'talent' or 'skill'.
There are little changes between each level, because the characters are not what keep you alive. It's you as a player that keeps your character alive.