I'm not sure about Divination (I played very little KF, and it was long ago), but it sounds about right. While it may look unbalanced, Charm and Compulsion effects are relatively common and usually REALLY DANGEROUS. So while the saving throw protects against only a few things, those few things are something you definitely want to be protected against.
Yeah, that's kind of what I thought. I dunno, it kinda rubs me the wrong way. I'm really not a big fan of "this stat is not useful, but if you don't invest in it you will die" type things. That's basically why Constitution went the way of the dodo as well. It's like, this stat does absolutely nothing except provide more hit points and Fortitude. Has no appreciable skills, little to nothing is keyed off of it for players (monsters at least get better poisons and breath weapons if they have 'em), etc.

Feels a bit like spite to me. "Here's a score that's useless so to justify having it we made new, terrible penalties if you don't, but beyond now having to have this to avoid losing your character, it's still useless".

Seems a bit like the old honey vs vinegar adage.