Honestly, I feel the level restrictions make more sense if you are tied to one path in the final game. Like. Go through the underdark or over land. But you cant do both. That way you wouldnt (or shouldnt) get enough XP to even reach those milestones. It would also mean were more 'rushed' if you will, but in the grand scheme of the game it makes sense.
For testing purposes though I would love to be able to check out lvl 5. I want to see the insane power of fireball (which is designed to be OP in DnD so it should be :D), I want to check out multi classing, I want to see fighters (and other classes) with multi attack etc. etc.
If were meant to help with balancing I feel lvl 5 and up is also part of that
