As someone than came later to the disscussion, and read some of the Kamala comics, (and liked) I would say than Kamala became popular depiste being an inhuman character. What I mean is being an inhuman character didn't help her popularity, but didn't was detrimental for her, either.
Being an inhuman is less important to her than being muslim. Being inhuman would be relevant for her character if she would had started as an inhuman character in the inhumans books and if her world orbited around the inhumans situations and plots. From what I read, most of Kamala situation were about her life, her family and her neighbordhood and school. Her most regular contact with the inhumans were Lockjaw. But maybe it was my mistake and I had not read the more inhumans driven issues. But from what I read, the inhuman aspect was something non existant.
In the Kamala case, that would be the same. If she (or Moon girl) would had debuted earlier or later they would had changed to those other times circunstances, it was the trends of the moment, but other elements, as her muslim identity would had been keep the same. I remember an interview were the creators of Moongirl were asked to made her an inhuman character, and they had not problem with that because that trait was not thet relevant to their character (I think I read it in Bleeding Cool years ago, if you want to check). So the case of kamala is parallel. Being inhuman is not that pivotal. The point is than you can change her (Kamala) from being an inhuman (and if it is done, most probably Marvel could wanted to make the Kree connection more direct to her) and that could be a minor change. But, on the other hand, if you, for example make an issue about Kamala becoming christian... then you would really have hell$#!+ and fire.
On the mutant comparative there is a particular difference: Many mutant characters became famous after they debuted in the x-men books and then they migrated to their own books, but I hardly remember the opposite case. Maybe there are but I don't remember anyone right now. Kamala started in her own book and then it was said she was an inhuman. If she would had spend one or two years as a member of the inhumans books as a character in development, I would agree than being inhuman is a relevant part of her identity.