Oh boy
I was waiting to get to lvl 16 to go to Skellig and do the Destination: Skellige quest and another one that is lvl 11 suggested but now I think I'm late as I'm lvl 14 already.
Yesterday I did a quest and got 5+5xp, now I understand why.
It may not break the game, but you have to admit it's PRETTY frustrating to spend an hour or so and get like 50xp for the quest. Ok, maybe the monster you had to kill wasn't that difficult at your level, but you spent a lot of time doing it. What will happen is that people will skip low level quests because of a bad designed xp system.
It would make more sense if you needed more xp to lvl up as you played, just like every other RPG. This "fixed xp" system ends up fuc#$% a lot of the game experience, in my opinion.
Even though, even with all the problems this game has I JUST LOVE IT, you CDR Projekt Red bastards.