First of all, just because they're a trio of female protagonists doesn't mean it's going to be a yuri focused on them with minimal involvement from other characters. This is "Deku hangs out with guys more so MHA must be BL" level logic lmao. Secondly, again, the problem is not in the shipping itself. It's just that I hear references to it so often that it's starting to resemble a series of infamous ships that started out as a joke but ended up as a very intrusive OTP. The manga will focus on their interactions anyway, because again, they are the three protagonists of the story.