As far as I understand it, the balancing problems are due to enemy health and damage bonuses if they are a certain level above you, and penalties if their level is a certain number below yours.
Personally I think this is really ridiculous because it means as Geralt levels up, not only does he gain buffs in terms of armor and weapons and skills, but lower level enemies get a huge reduction in their health as well! And with high level enemies, if they are 10 level or more above Geralt, they get a HUGE health bonus. As soon as Geralt then levels up once with a 9 level difference, suddenly that bonus is removed from the enemy, making it mush easier to kill than one level prior.
I am currently using a mod that simply removes those bonuses and penalties from enemies and already I find that the game balance is MUCH better!