For me it's a bit more nuanced, because directors, just like the medium itself, I feel are allowed to (and even should) change and evolve. I know many folks, both in the industry and out of it, love to pretend that movies are some giant, elite art form, and granted, oftentimes they are. Some films are genuine works of art, others are well-made fun, others are dumb fun, and others are just slop. There's room for all of it, and just because a director might cut his teeth on one form doesn't mean he shouldn't be allowed to try something new, or even pursue a passion project. Being able to direct and produce really well-made movies doesn't mean that you necessarily have good taste when it comes to your personal life; sometimes you get Del Toro's Frankenstein, other times you get Megalopolis. But we definitely pigeon-hole directors just as much as we do actors or singers.
Like others have said, Edgar Wright's movies have always sort of been cult classics, aside from a few notable hits here and there. Shaun of the Dead, obviously, but one could argue that that's just as much- if not moreso- Simon Pegg's accomplishment than his, and even then, the movie is still something of a cult classic. The vast majority of his movies have shared screenplay credits, and many utilize pre-existing properties, so while undeniably his, they also share someone else's DNA. That said, where the man definitely exceeds is style- his movies are all very fast, frenetic, and fun, sometimes to the point of exhaustion. But you could also argue that he leaves a very unique fingerprint on the film landscape and utilizes the medium in ways that a lot of others don't, blending motion, music, editing, etc. to make a very tightly-made film. Doesn't equate to "good", obviously, but I don't think he can be accused of being a lazy filmmaker. I, for one, would consider Scott Pilgrim one of my favorite films, and while it's an effort by many that makes it so, it's definitely in large part to him.
But, to go back to the original argument, obviously Cameron's films have simplified a bit over the years. Love them or hate them, you can't deny that he puts a lot of thought into them- effects-wise, lore-wise, etc. It's beyond clear that the Avatar movies are his passion projects. I suppose you could say the same about most of his projects- like Del Toro, they all revolve around something he's overly passionate about; some directors are lucky enough to have their passion projects really connect and pop off, while others have to trade one big studio tentpole for a smaller passion project. Every filmmaker has their "dud"- even Spielberg has had some lesser films; I think the "why" is just as important as the "what"- did the director really have that much say over the finished product, or is studio interference, budget issues, difficult actors, etc. to blame? Heck, some directors are criticized because they continue to make the same kind of movies, whether the quality declines or not. They don't change enough with the times, and the formula that once worked really well for them is now considered stale, ironically because a lot of times, other directors will copy their style- often to a lesser extent- and the audience grows tired of it through them, not the original director.
Point is, quality is completely indicative of the times, and the times are always changing. What's good now may not be good ten years from now, and what sucks now might get a retrospective assessment down the road and be considered ahead of its time. Nowadays, films are considered a "bomb" if they didn't do well at the box office, regardless of quality or if they find an audience on streaming, so many great films are just completely disregarded due to things outside of their control. Either way, though, I think there's room for all of it, and I don't necessarily think it's fair that big-budget popcorn flicks are often held to the same standards as the more refined Oscar-bait movies. These days, opinions are a dime-a-dozen, and everyone wanting to both feel like theirs is important or feel like they have to fit in with others and are thusly ashamed to admit they like something others may not, it feels like everyone is an armchair expert on movies. And don't get me wrong, I'm every bit as guilty of it as anyone else.
TLDR- I think we may be being too hard on movies. That may feel like an ignorant, stupid thing to say, but I do feel like the old metrics with which we judged movies need to be re-assessed a bit.
