Isn't this like the "True Grandmastery" components already in the BG2 Tweak Pack or whatever? If so, I'm sure it also mods the relevant strings. Seems kind of overkill for the BG2 engine though if you ask me (which is probably why they changed it from BG1 to BG2).
Something like that, yes. The problematic mod isn't BG2 Tweak Pack however, but TDD. In my game TDD is the only mod to have altered wspecial.2da, but apparently it doesn't update the relevant strings with corrected values. Since TDD is no longer supported (unless I'm mistaken) I thought this would be a natural job for the Fixpack.
I agree about the overkill part, but I think the bonuses was too nerfed with vanilla BG2. Should be something in between maybe.