>>86158752OP here.
I fully admit, when it comes to comics in general, I'm pretty casual. But I have actually read a respectable amount of Capt's stuff, old and new.
I didn't have an issue with brat Billy because I thought it was a way to change things up without going too far or being an obvious cry of attention. It gives him a chance to develop into the Billy we know more. I don't think changing up a character is inherently bad, especially something that isn't all that radical and can be used as as stepping stone.
The name change sucks, I'll always properly use Captain Marvel, but admittly Shazam is easier to say and type, so I use that a lot too.