Obviously, you’re a Captain Marvel/Shazam fan, and I understand your consternation that a Marvel Comics character has absconded with the name of another hero who’s been around for 80 years. But here’s the main problem: Everyone else knows him as Shazam. Okay, there is a certain portion of comics fans — I would say way less than half, of which you are clearly one — that feels like Billy Batson is the One True Captain Marvel, but the rest of the general populace literally thinks the character’s name is Shazam anyways.
It’s all because of the rights issues, and mainly because how Marvel Comics has the rights to the name Captain Marvel. Fawcett, publishers of the original Captain Marvel/Shazam comics, stopped making them in the ‘50s. In the ‘60s, Marvel Comics trademarked the name Captain Marvel for their own Kree alien superhero, which meant when DC licensed the Fawcett characters in 1972, they had the Fawcett character named Captain Marvel, but couldn’t call the comic Captain Marvel, so they used his transformation cry “Shazam!” for the title.
This extended to other media as well — DC could not promote the character as Captain Marvel anywhere, even though the character’s named was Captain Marvel. So when Billy Batson made his TV debut in 1974, his show was titled Shazam (okay, The Shazam/Isis Hour, but you get the point).
That’s 40+ years of marketing the character as Shazam, and that’s how he’s known to pretty much everybody. Hell, even DC finally gave up when they did the New 52 and finally just renamed the character Shazam, just to cut down on the confusion, and I think it was a smart move. Point is, if even DC calls him Shazam now, he’s Shazam. This battle is lost.
Which brings us to Marvel’s Carol Danvers, and whether she should be called Ms. Marvel or Captain Marvel in her movie debut. I have to go with Captain, because 1) that’s her name now, 2) she was originally named Ms. Marvel to differentiate her from the original Kree Captain Marvel and the Kree Captain Marvel isn’t part of the cinematic universe, and 3) calling her “Ms.” just seems kind of condescending. I mean, it was standard procedure when the character was introduced in 1968, and then the name stuck. But to introduce Carol Danvers to the cinematic universe in 2015 or later and then for everyone to call her Ms. Marvel just seems weird to me, for all the reasons above. Calling her Captain Marvel in the comics was a long time coming, but it was overdue, and there’s no reason to start her out as Ms. in the movies.
If it makes you feel any better, I’d bet $100 that if/when she makes her movie debut everyone calls her “Carol” 90% of the time anyways (and then Tony Stark calls her “Ms. Marvel” at one point just to be annoying).