Well he was cut for the same reason Zach Hilton was (yes, blocking isn't his forte). Early on especially it appears Payton felt the TE had to be heavily involved in protection schemes (the TE has).
As Stinchomb and the O-line in general has improved though the TE has been released into the passing game more and more. So when Conwell went down it appears they went for Billy Millers recieving ability.
The TEs that Payton brought here have done an excellent job. Dan Campbell, Billy Miller, and Nate Lawrie have each shown to be all reliable blockers and pass catchers. Campbell, in particular, has made some huge catches for us this year.