I agree on the movies having to offer interesting characters and stories.

But I don't think marvel comics are running dry in that regard; there is still loads Disney could plunder from the comics

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.

I think your view is clouded by hindsight.

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