After reading this I am very confused. I stopped reading DC just after COIE and took a break for twenty years because I didn't like what DC had done to my beloved characters. I didn't know that the current version of Captain Marvel has actually been around since post-Crisis.
https://www.cbr.com/shazam-billy-batson-same-person-debut/
Are you arguing against the late 80's version of Captain Marvel that seems to have dismantled everything that came before it--or are you just against Johns' version? Because to me they both seem to be in defiance of the original Captain Marvel character.
The Captain Marvel of Post COIE was nothing like the current Geoff Johns version. The current character named Shazam debuted in 2011, and his backstory, personality and supporting cast are completely different. That CBR article is about how the golden age Captain Marvel used to be portrayed as having a different personality/mind to hm, separate from billy Batson, but that isn't relevant.
The biggest difference between pre and post COIE Captain Marvel is honestly the depth of the character and his stories. Regardless of what some Shazam fanatics think, post COIE Billy Batson had a lot of depth and nuance to his character, he just did it without being a generic angry teen. It also kept supposedly goofy stuff but did it really well (Mr. Tawny is an actual character still, for example). It even made the wizard Shazam more of a character then he has ever been in any other incarnation
There are basically four versions of Billy Batson/Captain Marvel in the comics. The golden Age version, the Pre COIE DC version, the Post COIE version, and the Geoff Johns version. They're all different, but the GA, Pre COIE and post COIE versions share similar "DNA", and they're the versions I really like. They keep a similar "spirit" of the character if that makes any sense. even though they have noticeable differences, they still feel like versions of the same character who has evolved over time, like most characters that started in the Golden Age and continued to the modern age.
I may enjoy the movie and its take on Shazam, but comic wise Shazam is always going to be inferior to Captain Marvel in every aspect of his character to me. I have mostly decided to refer to them as separate characters now. My favorite superhero of all time is the original Captain Marvel in general, with the post COIE version being my favorite version of my favorite hero. Shazam is a character I like in the movies and tolerate at best in the comics.