I think it is clearly the exception rather than the rule when it comes to college players. Take the player that is widely considered to be the top college bat this year. Nick Banks at Texas A&M. He's a very good college hitter, but the tools simply aren't there for him to be a high level pro hitter. You are probably looking at a Brett Gardner type who is going to be drafted a lot higher than he should. He is similar to Ian Happ from this past year's draft, who many Braves fans wanted Atlanta to draft. Ian Happ is not going to be an impact pro hitter.
A.J. Puk is a guy who could still have significant ceiling left in him. He is a power lefty who really didn't start coming on till later in his sophomore season, so there is still room for growth there. Still, I would favor Riley Pint and Jason Groome, who I believe both have a higher upside.
Comparing pitchers and hitters if foolish. Even then, most top 5 college picks make it to the majros, can't say the same with HS players. Let's look at a 3 year sample where a HS player should be up by now, say 04-06 It's the internet, I'm sure you'll sight sample bias, I didn't pick these years in advance, these are also early internet pre-smartphone era drafts as well where the insane amount of info we have today wasn't readily available.
04 draft featured 2 HS and 3 college players. Number 1 pick Matt Bush(HS) couldn't make it out of A ball, Number 2 pick Justin Verlander is a bonafide ace, number 3 pick Philip Humber had a pretty bad major league career but made it, number 4 pick Jeff Niemann had a mediocre major league career, and number 5 pick Mark ROgers (HS) was about the equivalent of Humber,
05 Draft had 1 HS player nad 4 college players. Number 1 pick Justin Upton (HS) went on to be a major league star, Number 2 pick Alex Gordon had a rocky starty but has turned into a really good player, Number 3 pick Jeff Clement sucked in the majors, Number 4 pick Ryan Zimmerman for a bit was one of the best 3B in baseball until his shoulder went, number 5 pick Ryan Braun is one of the best right handed hitters in baseball.
06 Draft was all colelge players. Hochevar had a mediocre major league career, Greg Reynolds sucked in the majors, Evan Longoria has been one of the best 3B in the majors, Brad Lincoln has barely been above replacement in the majors, and Brandon Morrow has been a solid major leaguer.
IN that sample you had 3 HS kids taken, one star, one decent and one bum. You had 12 college kids taken, 5 are stars or great players 2 really suck, some are solid some are decent.
For fun I'll keep going though just not roll it into my counting total
07 - 2 HS players 3 college, all got ot the majors. Players ranked in rWAR go David Price, Matt Wieters, Mike Moosetacos, Daniel Moskos, Josh Vitters
08 - 2 HS players 3 college, All got to the majors, players rand in rWAR go Posey, Hosmer, Alvarez, Matusz, Beckham
09 - 2 HS players 3 college- All college players go to majors no HS, ranked in rWAR Strasburg, Ackley, Sanchez, Tate, Hobgood (last 2 DNP obv)
10 - 2 HS palyers, 2 college player, 1 juco - Harper, Machado, Pomeranz, Colon, Tailon didn't make majors
11 - 2 HS players 3 college - 1 HS and 1 colelge didn't make bigs yet (though one who did from HS was Bundy who the orioles brought into the pen in 2012 and sent him back to develop so doesn't really count IMO) Ranked, Cole, Bauer, Bundy, Hultzen/Starling
12 - 2 HS players 3 college - both HS players got to bigs, one college did not. Correa, Zunino, Gausman, Buxton. Zimmer
Basically my point is this. The top college players are usually really good. At worst they make it to the bigs. Some top HS guys don't work out at all. Of course some are Machado as well.
Worrying about potential isn't the important thing, it's who will be the best major leaguer. While you sometimes lose a bit on ceiling in a college guy. As my list proves, sometimes colelge guys like Strasburg, Verlander, etc. are really great.