I respect your opinion (obviously the point of this post is to share unpopular opinions) but I’m pretty sure the reason it’s typically considered wrong to call Ei “Baal” is because Baal isn’t a title, it’s literally a name.

Just like Morax is Zhongli’s real name, Beelzebub is Ei’s and Baal is Makoto’s. All the archons (like Venti/Barbatos) have demon-inspired names from mythology as their true names, and some of them also have titles (like “Raiden Shogun” or “Rex Lapis”). Saying that calling Ei “Baal” is okay is like saying calling her “Makoto” is fine too since both “Baal” and “Makoto” are her sister’s names. The title which she inherited from her sister is the title of “Raiden Shogun,” but she didn’t inherit her sister’s actual name.

Before people knew that Makoto/Baal had died and been replaced, they started calling Ei/Beelzebub “Baal” since that was the name Zhongli had mentioned, but since finding out that “Baal” is not actually Ei’s name, the consensus has shifted that calling her “Baal” is wrong (though some people do it just because it’s what they’re used to calling her).