Consider it like dealing with:
a) ... Einstein - Physics Prof
b) ... Weber - Sociology Prof
c) ... Smokey Yunich - the best nascar mechanic ever
Each of them could be considered above max Human intelligence.
Older editions of d&d had an 18 Int = 180 I.Q.
These guys would be way over that (perhaps - we don't know for sure / this is fantasy anyway).
Einstein is a Wizard, but won't bother with trying to explain how birth rates should go up/down.
Weber is an Archivist, and can do the birth rates thing, and hangs out with clerics (real life too).
Smokey is a Factotum, he can build Einstein's goodies, even if Einstein can't.
But ask any of them, what D&D 3.X rules are, they know nothing ...
Or if a Knowledge Local check can help certain negotiations. Sorry no ranks = who are the Huns?
Barring a decent divination to these boards, eh.
Int of 20 doesn't make you demi-god-like,
it makes you really good at what you do,
and
not really good at all sorts of other stuff.
Dude with a college Math teacher degree, is miles
better at math, than 7th grade pre-algebra students.
But not a genius, and not necessarily "smarter" than the Drama teacher (HA !!).
Wizard 10 with Int of 20, is miles better than apprentice Wizards with Int of 14.
No ranks in 3.0e scrying and no magic ball = no fun divs.
etc ...