Also, I agree that some enemies cheat. It seems Daedalic was uncomfortable with how their rules worked and didn't mind manipulating them...
Hm, that's a pity, I don't like such stuff. At least Daedalics implementation (blatant cheating when displayed 90% is not "real" 90%).
I can live with and prefer insanely buffed enemies (which they also use, e.g. the pruple mobs in chapter 4) that otherwise adhere to the rules - when there's a reason for such enemies, at least.
The other thing I wonder a bit about is the magic resistance. Even with (for TDE PnP) very high values the enemy does not see a reduction in casting chance. So I guess that either they have very high values both in the respective spell and the governing attributes, or the game is cheating there, as well.
In priciple one can just ignore magic resistance - it's barely used at all up until the beginning of chapter 4 and then you should be strong enough to do without it as well.
However, I wanted to see if I can interrupt enemy spellcasters with high magic resistance and how much I need, so I started buffing Naurim. I'm now at ~15 and enemies still seem to have 95% chance for level 4 spells that affect all my chars.
Edit:
Thinking about it a bit and doing some calculations, the effect of MR indeed is pretty small when enemy casters have high attributes and skill levels. So it might just be a balance issue there. Not that we will ever see some balancing patch for BG1, but to me at least the effect of magic resistance seems too small considering how costly it is to raise eventually.
It does seem an all-or-nothing thing. If you want to raise it, put a lot of points into it, otherwise ignore it and use the XP for different stuff.