Heh - yep.
I liked the limited and fixed amount of experience you got from the game.
You got 0 XP from summoned creatures, but what about flying things spawned from the nests in flying towers? I never checked, but I assume you get none for them either, otherwise that'd be infinite XP right there, just by wiping out all ballista towers and all nests but one, then kill the wyverns all day.
Or maybe there's a limit to the number of wyverns each nest can spawn?
If nest XP is fixed, then it feels like it should be possible to calculate the absolute max number of XP a min-maxing playthrough could generate, assuming the player by done all fixed-XP stuff at the last moment possible (handing in quests, destroying ballistas), and did sliding-scale-XP stuff as early as possible, always selected those quest options which gave the most XP in the reward, reloading many times to get magic items of +1 Wis from chests/quests, etc. There'd need to be fine tuning to ensure that critters were killed in the right order (eg ducks should be killed last, since they're a fixed XP reward: but rabbits, while fixed, should possibly be killed as soon as you're able to damage a level 20 creature fast enough). There might also be tradeoffs like "handing in the Creature quest early to get better damage means you get higher DPS and so can kill more powerful creatures earlier".
Competitively Minmaxing XP could be something that could make for replayability: it'd add a new challenge
