I agree with points one and two.
For point three, to me it really doesn't make a difference between requiring 100000 XP to next level and the enemy giving 100 or requiring 1000 experience to next level and the enemy giving 1. In Divinity 2 it also worked both ways: killing enemies of higher level than you gave more experience. There should always be a minimum experience gain, though. Like the level of the opponent or something.
Getting 100 experience for lower level creatures might seem more rewarding than getting 1, but it doesn't mean that killing lower level creatures is any more meaningful. You still need to kill 446 of them to level up.
