Let’s be real, it’s just Zoro and Sanji fans complaining here.
I think practically everyone (especially post Rocks) is fine with the idea of Blackbeard being strong enough to be the final villain of Luffy.
(note that this is just the idea of him having the strength, not that he will be. I.e. even people that think Imu is the final villain still think EoS Blackbeard will be a monster)
Fans of the other Strawhats are reasonably happy with a Blackbeard Pirate as well. For example, mid trio and lower trio fans know that realistically their faves won’t be beating the Gorosei. There was the HK’s, but the CoC is the weakness of them has rendered that nearly impossible. And there aren’t any good Marines for them to fight, no one gives a fuck about VA, even the zodiacs.
It’s just Zoro fans who want more than Shiryu, and Sanji fans who want more than Lafitte/Pizarro/Burgess.