@Xanhomey this has been said a thousand times before and i'll say a thousand times more: it's a useless distinction, a completely arbitrary one made by westerners. in Japan Yuri is used to mean any type of lesbian fiction. it means
white lily for christ's sake, purity is a part of the origin. reducing the term to only pornography is borderline insulting to the creators.
then you might say, there's no rule we should only follow the Japanese definition for genre labels, they can evolve. sure, but that's not my point. please peruse the Yuri tag right now and tell me if it's exclusively sexual content. no, that'd be fucking ridiculous in the first place. also, there are plenty of manga tagged shoujo ai with NSFW content too. so what the hell is the point?
also, often times the meaning of "shoujo ai" changes too. here you say it's "a story that focuses on their relationship", however i have heard "shoujo ai" used to refer to non-explicit yuri stories (otherwise known as "yuribait") or ones that end in "they are just great friends". this is the definition me and undeadclown were using. which one is it? no one can make up their mind
i am willing to accept shoujo ai as a genre label if
people would decide what the fuck it even is already. what are genre labels if not purely a marketing gimmick? if it helps people find the exact kind of story they want, it can be a useful tool. i'm not opposed to the concept of shoving off "lower-tier yuri (only subtextual implication of a gay romance)" into another label and only considering the "real yuri" as yuri. (even though, again, Japanese mangaka who consider themselves a part of the Yuri industry make plenty of stories just like that - Yuru Yuri is considered a seminal work and it's 95% subtext) but that's not how people use it right now, and the "shoujo ai is not porn and yuri is porn" distinction is, once again, absolutely fucking disgusting and i don't think it's necessary at all. (is the "ecchi" classifier not already a universal tag for those manga?)
(by the way that thraed i linked at the beginning comes to the most ideal solution: merge shojo ai and yuri into GL, and use the romance and ecchi subtags for those distinctions instead. this has been "planned" for over a year now apparently. i guess we will just have to be patient)