That is an issue to my opinion. I think XP gain should grow more exponential and start from very little figures (1 xp for lvl 1 monster), but with a buffer. Respawnable enemies would do, but only within some big quest (untill you kill some raid boss). If the XP gain is very exponential and you have respawnable enemy units, with some superhard boss, its fun. In warcraft3 they put a max lvl cap on each map. Why not make an 11lvl cap on a map where the strongest enemies have lvl 9, for example.
I didn't really think about xp buffer, but offered an idea of gold buffer,. Current XP gain would work well if the classes were more balanced.
