I'd argue there is a very big difference between "taking place in the real world" and having a realistic story, the latter of which is what I believe you are looking for. James Bond takes place in the real world, but I wouldn't exactly expect realism from it.
If this series was trying to be a realistic depiction of gay people, I'd be more inclined to agree with your statement.
I also agree that a lot of yuri stories have a trope where everyone is gay. In fact,
TV tropes has a specific trope page for this. It's fine to say that you don't personally like that trope (even I feel like it can be little overused at times), but you shouldn't correlate it to the setting.