There's no doubt the college commitment will play into PG rankings. Especially if it is from a high level program. Kids who already have commitments as sophomores and juniors are "projectable" and it is no real risk for PG to rate them higher than other kids who do not. But as 3AND2 noted, other factors come into play during any particular event and that can impact the ratings as well. There are no doubt lots of late bloomers who do not return to a PG event and are much better than their grade shows.
As most have noted before, the PG grades are not that big of a deal. The service is most useful for providing independent metrics on a players core skills. Those can give a college coach a starting point, but then a kid needs to perform in front of them to move the needle to interest.