I think people over estimate the Marvel brand. You can't just keep unearthing dozens and dozens of niche characters and comics and expect them all to have an established fan base.
Think, Disney.
Ironman? Yeah no shit. It's fucking Ironman.
Thor? Duh
Hulk? Yes, but get it right.
Antman? Pushing it but yeah he dope.
Captian America? Might as well said superman.
Gaurdians? Wonderful.
Captain Marvel. You lost me.
Eternals? ...
It's no mystery as to why not every franchise is going to be a hit. Just think about it.
When the first iron man movie was announced, the character was a solid b-lister
The guardians of the galaxy were even more obscure during a comparable timeframe and had a different roster.
So b-listers can be elevated by good movies and at the same time a-listers in the comics can bomb (Thor 2, Thor 4, non-mcu: Spiderman 3)
How well-known a character is in my opinion not the deciding factor for the success of a movie. I'd say the quality of a movie and the ability to build hype (which gets harder with what appears to be superhero fatigue) play a bigger role
Well, guardians of the galaxy had been very obscure, but I am not quite ready to call them e tier.
Remember blade? I didn't even know it was a comic book character when its success paved the way.
Really, putting the blame on the obscurity of characters is making it too easy and ignores all the fuck-ups around the movies that in my opinion have had a big hand in making them fail (not an exhaustive list):
Taking the worst trait from comicbooks: requiring the audience to have consumed other titles (worst offenders here are probably Dr. Strange 2 and the Marvels which need Wandavision and Ms. Marvel to make sense)
Alienating the (mostly male) audience: a big offender there is She-Hulk
Using fan service and cameos as replacement for good writing
pacing issues and tonal backlash: Thor love and thunder suffered from giving emotional moments not enough time to breath in favour of cramming in more laughs
Also don't overestimate how many moviegoers are also Comic Fans.
There is two things going on. You have opening night and you have total sales. Marvel has fully saturated Hollywood so they can't just ride the superhero hype for opening night. If the quality of the film is up to par like you said it can build momentum. What Im getting at is when I look at a Marvel movie you have to offer me something other than a canned action movie. When it comes to interesting characters and stories the well is starting to run dry.