My personal sign is when you start seeing awkward collaborations start cropping up. One time when I was thrifting, I picked up a graphic novel that had the Justice League, team with the Power Rangers of all things. I glimpsed into what the plot was about out of morbid curiosity and it was just a plain generic time and dimension thing.
Nothing ever connected between the teams at all. DC Comics, while fledgling at times with how they go about their series and movies, still have far more relevance than Power Rangers do. I think the Power Rangers are just grasping at straws to keep being relevant when people have largely moved on from them.
Which is fair, but you could also say the same thing for the Avengers. They both started out weirdly like making you think “what the hell do these guys have in common with eachother?” at first. Overtime, as comics developed, they became more established. Then it became more accepted and the rest is history.
But sometimes just pairing them up with say, my example, it makes it even weirder to where nothing meshes.
I would argue that the Power Rangers are not that odd of a pairing for the Justice League.
Quality of the work aside, both are superhero teams with complicated lore. They could use that highlight differences/similarities in ideology or methodology between the characters to create drama, before setting aside their differences to come together against a shared evil. The bones of a good superhero story are there.