I agree they aren't stars, but I don't think anyone suggested they were. But I also don't see underwhelming at all. There is a lot of room between "star" and "underwhelming".
With Cooper, Gallup, Lamb, and quality receiving RBs, there simply aren't enough balls to go around for every receiver on the team to maximize their abilities, and even so, Schultz was the 12th leading TE last year in terms of yardage, and that was with him not beginning the year as the starter and with backup QBs most of the season.
In a different situation I think Schultz could be an 800+ yard, 6 TD TE. And who knows about Jarwin? In his limited opportunity in the past he looked to have the ability to stretch the field from the TE position, but we can't say too much because he hasn't had the chance to show himself the way Schultz has.