I played through the game as a dark-side soldier/guardian on medium difficulty and had absolutely no problems. In fact, it was a little too easy.
I'm currently playing through the game as a light-side scoundrel/consular on hard difficulty and it has been a more gratifying challenge.
I find it hard to imagine how any character could get to the end of the game and not have enough skills and experience to be ready for the end-battle. Even if you don't do any side-quests it still seems like you'd be really high-level that far into the game.
On an interesting note... mini-spoiler:
The first time I played the game, I named my character "Darth Revile" I found it cool that it happened to be so close to the name "Darth Revan". The dark-side was strong with me. This comment was edited on Nov 11, 10:36.
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