Fortunately, re: the bolded, the crowd of people who play D&D, and the crowd of people who demand that D&D be what it has so-called "always" been (read: what it was in 3rd edition), grow ever more distant from one another as the years pass and repeated attempts to re-do 3e "right" peel off further segments of the 3e-fan crowd.
Some stuck with 3.x (hell, some stuck with 3.0!) Some stuck with PF1e. Some went to PF2e. Some will--almost surely--stick with various versions of 5.x, or the myriad of 5e-with-serial-numbers-filed-off games, whether original or spurred by the OGL-invalidation debacle.
By comparison, the people for whom 5e is the only game they've ever known--and thus they have no special attachment to anything predating 5e's design--are a growing bloc, and a lot of them recognize issues in the design. I think your confidence that D&D is so "locked in design wise" is, if not misplaced precisely, then at least reflecting design trends from over a decade ago--pushing two. By the time 6e rolls around, because you KNOW a 6e will eventually roll around, the vast majority of D&D players will be those who started with 5e and know the problems 5e deals with. They're going to want things which address that, not things which address "tradition" that started before they were even alive, by anywhere between three and thirty years.