I agree, it's possible his value would have been more justified had he been taken lower in the draft, but he just didn't look "special" in any way.
I am not saying he's a bust by any means, but rather he was not special enough to use a second round pick to get him.
Tight-ends get slower and bulkier in the NFL so if they are already maxxing at good speed level and already have muscle bulk, odds are they will get slower and bigger after a year or two in the NFL.
For example, compare these college highlight videos:
Which one of those players looks better?
The first one, they drafted with a second round pick.
The second one, they signed as an undrafted rookie free agent.
I would rather have the second one and my second round pick back (and that's not hindsight .. that's how I felt then about drafting Schoonmaker).
Again, I'm not bashing Schoonmaker because he's a good (albeit basic) tight-end, but your #1 and #2 tight-ends should be playmakers.
Your #3 tight-end should be your blocking tight-end and you can get one of those from the undrafted rookie pool or even convert a college lineman that couldn't make it as a lineman in the NFL to be your blocking tight-end.