In a way, you could argue that superhero roles, especially successful ones, have become both the most reliable way to "crown" a modern movie star, and the best way to show that star's dynamic acting range, since they get more than one crack at the character and good comic book movies require letting characters grow and change a bit more than a regular character in a regular movie would.
The trade-off, of course, is that its not the same type of "the actor is the brand" that old school movie stars were - the character is a brand in its own right, and may even end up a bigger brand overall, which might trigger some insecurity for some actors... but I'd also argue the modern market has allowed far more actors to "play against type" if a major franchise casts them if they so desire. Evans is a key example of that, especially since it could be argued that Cap was a role that played against his original "type" of character, and now he can demonstrate his skill at both unrepentant scumbags like Ransom as well as other, more positive characters besides Cap.
I think this is comparable to the impact of social media on music - the proliferation of new distribution channels means that more artists can get into the entertainment marketplace and make a living in it, but it also means that there's more categorization and recognition of when something is "niche," as it's premise and quality has to attract and hold new audience members rather than just be released by a larger distributor who loves the project.
This has sort of ramped up the old "Is this particular film failing or being less popular a result of it being niche, or is it a result of bad populist artwork drowning out quality material?" argument.
Personally... I think that professional critics and artists are just as qualified as large, mainstream audiences to declare what a quality film is or isn't - in other words, they're not actually qualified at all for that role. And a real issue for me is when a professional artist or critic declares tropes or cliches from their preferred niche to be "superior" to mainstream pop culture landmark tropes or cliches - no, a tragic movie about a privileged white guy that subverts expectations does not automatically have more quality than a comedic adventure movie, and film teachers need to stop pretending that obscure French Cinema has some greater impact on society than it actually did by inspiring others to make better, more well-known films. In fact, it need sot be acknowledged that sometimes trying to appeal to a more niche "critical darling" style of film-making can actually create an even more shallow, more pandering movie (The Last Jedi) than a blockbuster crowd pleaser that actually has much more artistic merit in spite of being so "fan service-y" (The Force Awakens.).
Blockbuster Popcorn Movies and Award Bait films are merely the initial form a film takes when the creator doesn't really know if it can grow beyond its original targeted audience - and it should be acknowledged that if an Award Bait type of film has mainstream success (like Knives Out) or if a blockbuster has a larger and more permanent cultural impact (the Dark Knight), then they *both* surpassed their initial forms, not just the first.