We’ve really had a tough time with #2 TE’s..
We’ve had one that could block but not catch, one that could catch but not block, one that killed a guy, and one that did none of those things and just kinda sucked.
It seems to me that BB sorta sees three spots/roles in the TE corps:
A) at least one guy who can both block and catch pretty well
.... a younger/healthier version of Bennett probably would've been acceptable, if there had never been a "Gronk"
B) another guy who can catch pretty well (an alternate red-zone threat), and can block
okay under certain circumstances (IOW, at least as well as a WR)
C) another guy who blocks really well and can catch for a first-down or TD on occasion (maybe 1-1.5 receptions per game, on average)
It really wouldn't require a whole lot of improvement in Allen's receiving to make him ideal for this last role. He doesn't really have that "B" guy at the moment.
Gronk has been and A+++ guy for several years and, if he retires, there won't be another one like him for years, at least not on the Pats. Expecting the next man up to even come close to what Gronk has accomplished will lead only to crushing disappointment and unduly harsh criticism. His "replacement" is likely to be a guy who ultimately contributes ~50-60 receptions, 600-750 yards and 5-8 TDs per season.
Right now, such a guy would be the "B" guy behind Gronk (as Bennett was in 2016).
But BB is likely to want a "C" guy as his base TE (in addition to an FB), for the sake of the ground game, more than for the passing game.