Just to point out, Hancock actually made a good $40m more than IM world wide.
Also, while IM1 is considered a "big one", I think that is in terms of quality, being a breakout and what it started (MCU), but in terms of money earned there's a good $500m between it and TDK, so I don't think it's a "big one" in that sense.
I think you're failing to look at other factors, such as film quality, marketing quality, production budget, as well as style/sub-genre. I think saying "amount x is sustainable but anything after will fail" is too black and white.
Like Dredd. IIRC, it didn't have good marketing, but also I don't think the GA even knows it's a CBM. They'd associate it with Stallone if anything.
GR2 was terrible, but offered somethin totally different.
Gambit isn't coming out this year. As others have said, TMNT isn't even viewed as a CBM by the public.
The GA also doesn't have to be persuaded to see all these films equally.
BvS & CACW are the 2 biggest hitters there by a large margin, with X:A firmly in 3rd.
Deadpool is relatively low budget ($65m) r-rated flick, if it makes $300m it'll be considered highly successful.
SS is mid-budget (I've seen ~$100m floated around), doesn't need to break the bank to be very successful.
But again, we aren't looking at 6 films all vying for $1bn here, they're various levels.
Wolverine will certainly be mid-budget, like the last one, that'll be aiming at $400m to be a success.
GOTG2 & JL are probably the 2 legit contenders for $1bn.
WW $600m, Thor $700m, Spidey $700-800m. And that's if they're all good movies that are well marketed.
It's actually not that different to this year.
If you look at the Worldwide box office of the last few years the top 20 films range from about $350m up to $1bn, sometimes well over $1bn with multiple films. So there's definitely enough room for these 6-7 films.
Again, you're not considering other factors, like quality. If DS sucks and then flops then no, fatigue hasn't arrived. It's just one instance of a bad movie not doing well.
If it's a great movie and still flops? Still not an indicator of fatigue, just one movie out of 6. The fate of the genre doesn't rest on the shoulders of one film.
And there's another point in favour of the Superhero genre, all 6 movies this year lean into different sub-genres and have a variety of tones. R-Rated action comedy, epic sorcery, grimey villain team-up, etc.
Even the 2 most similar in concept, BvS & CACW, are very different stylistically/tonally.
Same next year. And ultimately I think that's what it comes down to:
-Quality
-Variety (in sub-genre, tone, budget level)
-Good marketing
If the studios generally deliver on those then I think it'll be sustainable for quite a while longer.