So why are the studios concerned with fatigue then? Even with good box office numbers? You seem to have the answers
As Penguin points out, the studios are seeing fatigue in relation to every franchise that DOESN'T have a superhero in it (with the slight exception of Fast N' Furious.) Even usually dependable animated series like Cars and Despicable Me are in trouble, and The Mummy, Pirates, Transformers are all sinking fast.
But superheroes - this year has seen 4 so far (Logan, Spidey, Guardians, WW) and all have opened to critical acclaim and box-office success. WW held better than any superhero film since Sam Raimi's Spider-Man 2 - 15 years. Spidey was projected by Sony for an $80 million opening - it opened at $117 million, which partially explains the big second-weekend drop. The studios are so happy with superheroes, Fox, Sony, and WB are all increasing the number in their slate.
Now, will this last forever? No, diminished returns will come at some point, but these franchises fit the financial model of the modern Hollywood too well to go away for very long.
Some predictions - Marvel's Thor 3 will perform slightly better than Thor 2, Black Panther will surprise the industry with a significantly higher than expected opening, and Avengers 3, while not the biggest film of all time, will be as big as Avengers 2. Justice League will fall well below expectations, causing panic at WB, which will be alleviated when Aquaman exceeds expectations. Sony's silly Spidey semi-spin-offs Venom and Black Cat/Silver Sable will bomb and they will seek to expand their deal with Marvel. Similarly, Fox will continue to sprinkle clueless mishaps among surprising crowdpleasers, with X-Men: Pheonix doing poorly, New Mutants doing slightly better in relation to its budget, and Deadpool 2 making Fox fall in love with mutants all over again.
And Marvel will announce another ambitious slate next year, and WB will try to figure out why WW and Aquaman are hits and adapt as they extend their line, and Fox will go on as it has for a decade with hits and misses. And Sony will panic, because its Sony. Those are my predictions.
And I'm not sure people are even that tired of rebooted heroes if done well. I think, for instance, a new Superman that was "happy" and "good" would be a smash hit. Fox is kinda pushing the edges of this, though.
Oh, and sometime in the next decade we'll see a Tron soft reboot. And it won't fare very well.
