I don't see either comparison as valid, really. Gronk and Hernandez will probably never be matched as a pair, and we may never again find a TE like Gronk who can be equally effective on running and passing plays.
As for Graham and Watson, those 2 were known mostly for their blocking skills (despite Watson's speed), and my understanding of Henry and Smith is they're both better at receiving than blocking.
I think our new TE signings are good enough at blocking, but I hope no one expects they'll be as good as an extra OL out there because that won't be happening.
I'm reminded of that old document where Belichick describes his ideal offensive players for the system and he specifically says tight ends only need to be "helpful" as blockers, not dominant, so the new guys fit that description perfectly. That document also curiously says a TE shouldn't be cast aside just because of a lack of blocking skills...I wonder if that philosophy led to LaCosse.