Just my opinion,
If you're throwing 90 as a Juinor, yes you will have a very good chance to go off to a top end school, infact I would guess you are going to be recruited by many, many schools, and probably are gettign alot of invited to go off to camps this year. Also MLB teams will probably be in good contact with you. If word gets out about you.
A guy throwing 85 will also see a fair amount of attention and could also wind up at a DI, and even have contact with MLB teams.
FYI my buddy who in his senior year threw 83-86 in HS last year was told he would probably be taken in the draft on the second day, opted not to and is now at a JUCO but had many many schools make offers to him.
Speed is not everything.
In college you can find guys throwing 90+ in any level, but as you say you don't see too many of them.
But that also has to do with Redshirting due to injury, academics or the Coach or player feeling that they aren't ready to perform on the college stage just yet. Along with those guys being taken in the draft.
I can give you 3 examples of guys who throw 90+ Two didn't play cause of the Coach feeling that they weren't ready yet to pitch at that level, the third only got into 1 game all year.