Not to be a jinx, but all it takes is just one injury and suddenly this perceived surplus becomes quite the opposite.
Let's say that hypothetically the Patriots trade Hoomanawanui, and a few days later Ballard re-injures his knee. Until whenever it is that Gronk is ready to play that leaves the Patriots with just two players, Sudfeld and Fells at tight end. That leaves the team with no negotiating power, scrambling to add someone who will likely contribute very little due to not having spent any time with the club learning the system and terminology.
The Pats do not have an 'abundance of tight ends' just because one player from the group is likely to be cut eleven days from now.