Marvel getting desperate

The people (in this case, based on box office, the "entire world") seem to be making it known that they prefer clean air over polluted air. Therefore, it is nonsensical for Marvel to generate more polluted air (woman SS) for no reason other than "reasons", when the box office numbers show that people like clean air (known character, true to the character's nature and generally true to the comics).
I'm not buying this reasoning because the slowdown in box office revenue started after Endgame. You'd have to attribute what you call "pollution" to something else because woman SS isn't even a thing yet.
3 questions for you:

1. Is it a "contrary take" to want Marvel to remain true to their decades-established characters?

Not necessarily. That said, there are a lot of subtle and not so subtle differences between MCU characters and while there are important similarites there are also important difference. Nothing really wrong with either approach.
Why is it NOT a contrary take to change your characters completely from their established characterizations? Isn't that contrary to the character's history? Two-way street, I suppose. I agree that it would be a near-insurmountable feat to match the success of the Endgame era of the MCU, but they could have at least tried to do so by sticking with what worked: staying true to the character's nature and generally true to the comics.
Keep in mind Kevin Fiege is a comics reader and knows the lore well. That said, he adapted characters from the Comics to the big screen. Some have liked it, and others not so much.

2. How exactly does Covid necessitate changing SS to a woman?
It doesn't. At least not directly.
3. I agree that box office slowed dramatically during and post-Covid and studios had to pivot and all of that. Does that explain The Marvels box office being 1/8 the amount of Guardians of the Galaxy Vol 3?
i think there are myriad reasons. Movie going in mired in a pretty bad slump, and The Marvels got hit by that trend. That said they've been outperformed by a couple of features. That's not good for Marvel.
They marketed the hell out of it, Beastie Boys in the (high energy and funny) trailer, Disney Plus TV tie-ins. Yet there it wallows, at the bottom of the heap.
I dunno, they did market it some, but it wasn't plastered everywhere like Oppenheimer and Barbie in the middle of the summer. Others get the enthusiasm for it because they haven't watched Ms. Marvel or Captain Marvel.
Gosh, if only Marvel had decades upon decades of established storylines from countless writers and artists to pick and choose from. Oh well, maybe in another multiverse!
They have done that to some degree. What do you think they've been doing the last 15 years?
Lastly, any comment on my replies to your Jane Foster, 1960's straight men, etc points?