You're comparing an era where the vast majority of superhero content was being held in a very low regard by society to a time where it is at an absolute high, making billions and dominating the box office every year.
Similarly you are comparing a time where we've had around 20 superhero flicks in the last three years (without even taking into account the countless TV shows) to a time prior 2000 where they didn't even have 20 theatrical superhero films overall. What's the point of saying that those successes were not in the same year with all these taking into account?
When someone is making an overall judgment over very different situations he makes it in relative, not absolute way. So at a time where studios throw more money and resources than in any other movie genre and audience loves them more than anything, to have a year where five live action superhero movies were released and 80% of them are box office and critical bombs (with more to come) certainly showcase one of the absolute worst years, yeah.
As for thinking Quantumania is better than Superman: The Movie, opinions are subjective, but that's certainly a take.
A) You're acting like the genre being held in low regard was some outside uncontrollable factor. The genre was just mostly ****. That's why people held it in low regard and that's why most superhero movies failed. These two things are directly connected to each other and the people making those movies back then carry just as much responsibility for that as MS does for Quantumania and WB does for the current state of the DCEU.
B) If you seriously think there weren't 20 theatrical superhero movies total prior to 2000, you're woefully uninformed. There weren't anywhere near 20 *good* superhero movies, but there were more than 20 total. In fact there were multiple superhero movie releases most years going back to at least 89 and a few years with multiple releases even earlier than that. As far as I can tell the last year a superhero movie wasn't theatrically released at all was 1988, and the last times before that were 1985, 1982 and 1979. It's only prior to 78 that it was normal for there to be no superhero movies released in theaters in most years.
And the point of saying those successes didn't happen in the same year is that you set the scope of the conversation at 'the worst year in superhero history'. So it's obviously ridiculous to say the pre-2000 era wasn't so bad because a movie released in 1978, one released in 1980, one in 1989 and one in 1995 were all succesful. They're literally decades apart, with lots of years in between in which not one single superhero release was actually successful (despite those years still having superhero movie releases).
C) How much money Marvel and DC have thrown at these current failures makes the situation worse for the companies themselves. It doesn't make those movies' level of failure worse compared to older movies which had lower budgets but also had much lower box office. They're still all failures, some spectular ones, some moderate ones.
D) Your insistence on counting movies that haven't even released yet in your assessment doesn't paint the rationality of your argument in a good light. I expect Aquaman to probably crash and burn like the rest of the DCEU, myself, but until it actually happens it would be absolutely ridiculous for me to include that as evidence of anything whatsoever.
E) As far as 'a year where five live action superhero movies were released and 80% of them are box office and critical bombs', let us look at 2004. A year with five live action superhero theatrical releases - 1 hit (SM2), and everything else grossed less than the Flash even adjusted for inflation. Hellboy is kind of a cult classic, but not exactly super popular. Blade Trinity, Catwoman and Punisher are famously hated.
Nobody's saying this is a great year. But trying to call it the worst year in the history of the genre is still ridiculous. There is still actual success in this year, and unlike 2004 or most of the years prior to 2000, that success is not limited to just one single film doing well (no matter how much you insist on trying to cut Spider-verse out of this conversation for no good reason whatsoever).
ETA: Found some weird errors in one of the sources I was looking at so I went back checked all the numbers against other sources. All the numbers I've used still seem to be right, but I did realize that The Incredibles also was a 2004 release so, for the moment at least, 2004 is actually a very similar year to this year, not really a worse one. We'll find out soon enough how Aquaman and The Marvels change that.