DC had their chance with the Captain Marvel name and lost. They took the rights from Fawcett comics, and as a big FU they purposely shelved the character for years. Then when Marvel came along with their own Captain Marvel in the 60s, DC couldn't do anything about it. So, if Shazaam fans are still pissed about Marvel having the rights to Captain Marvel, then they should be pissed at DC.
Do you have a link to whoever said this about Carol? I would like to argue with this person.
Edit: I personally don't like the idea of both characters sharing the same name, because whenever I do a google search of Captain Marvel, I do not want to see Billy Batson. Also annoying, my Captain Marvel searches sometimes yield results of Captain America.