My unprofessional opinion is the more linear your arm swing and release is, the looser it needs to be. The more vertical, the tighter, because you can get away with it.
I get tweener revs on the ball even with a very elongated, extended follow-through and a good deal of forward-projected loft. But in order for that to work, I cannot stick in the thumbhole. If I do, I'll lose 7/8 to 9/10 of my rev load at release. My release works when I can combine a late thumb exit with an easy thumb exit.
It's just been over the last two years that I've been able to stop knuckling the ball, but I've done that through discipline and practice. If I tried to tape my way out of it, my thumb would probably be in the rafters of my local bowling center right now.
For guys who hit up on the ball at the line or have a heavy vertical component to their release, I could see them being able to have a very tight thumb hole, because they could leverage their way out of it. Not so for guys like me.