I usually kill those 3 level 5 cambions at the start, I also get the killing blow on the squid for 50 extra exp too.
Thats 120x3 exp + 50 exp. I usually hit lvl 3 by the time i free Laezel from her cage.
Most people prolly wont try to play/cheese this encounter that way, but even still id say yeah leveling up is a bit fast at the moment.
I hit lvl 4 by the time I complete the village goblin + ogre fights.
Cant say im surprised that you managed lvl 8
