I agree that he's obviously been improving, but I also think it's somewhat difficult to try and put a "real" value on a player so early on in their rookie deal.
There are examples, of course, such as the 2 TEs a couple/few summers ago--although that very well may have occurred prior to the new rules of the most recent CBA. I'm not certain either way, to be honest.
The good news, as you've mentioned, is that Jamie Collins has seemed to improve in certain areas throughout his first 2 seasons here, so hopefully that will continue!