So he is basically an overpriced OL. I hope they cut him next year. I know how good a blocker he is, but you can use a Fleming type of player there and it will cost 1/5 of Allen and have 80% of the production. They really need to let Hollister go too and draft 1 or 2 TE. Gronk is not gonna last 3/4 more years.
Allen is an "overpriced OL" compared to a guy like Fleming only if you think he's exclusively used on running plays. The Pats run a lot of play-action with Allen in the set. And, on those plays, Allen quite often runs a legitimate route (not just drifting out into the flat). That's not something that a Fleming type player is likely to be able to do. It doesn't matter a whole lot whether or not Allen is targeted on his route, the defense still needs to devote a resource to cover him.
I'm not saying that Allen is worth his $7.4M cap hit to the Pats in 2019, just that they're not going to get "80% of Allen" out of any OL at any price.
Just last season, Belichick himself stated that TE is certainly the most difficult position the learn in the Pats offense, aside from QB. The reason he gave was that a TE needs to learn the OL blocking calls and reads the same as an OL would, PLUS learn the routes, reads and options pretty much the same as any WR would. They're basically tasked with attempting to master two completely different positions at the same time.
It's certainly bad that Hollister has been unavailable the season due to injury (out 5 of 8 games, so far), especially after he was healthy throughout last season (his rookie year). However, he's still one full season into that steep learning curve and, according to reports out of Camp (even from the more trustworthy media guys), he appeared to have made something like the legendary "second-year" leap at both the blocking job and receiving job (and he had already developed into a valued special-teamer last season). So, arbitrarily dumping him to bring in another rookie TE or two in 2019 might mean that the Pats wouldn't have another young,
productive TE until 2020.
It's highly unlikely that the NFL will see another TE of Gronk's caliber and "completeness" for many years, especially considering that, nowadays, college TEs who are good receivers are rarely even taught how to block. They're pretty much all starting from scratch, including Hollister. Anyway, expecting the Pats to be able to "replace" Gronk in the next draft or two or three is like expecting to hit the Powerball jackpot.
What's likely to happen instead (IMHO), is that the Pats will reconfigure the offense around a lesser talent or two who they've developed into "complete" TEs, but who won't ever be in the same kind of "starring role". When Gronk is gone, his starring role in the offense will simply cease to exist. And, given the likely developmental lead-time, the moment for the Pats to start acquiring and developing those guys was during the 2017 draft (with Hollister) and the 2018 draft (possibly Izzo), not next year.