Completely get it. I also don't like when an author uses an identity just for the sake of having said identity. Plus false stereotypes. I don't mind people using a stereorype to make fun of the stereotype or if they add 1 character extremely feminine or masculine as long as they make sure to let the reader know that is not the norm.
Like you said everyone is super diverse and there are a lot of different people even if they are categorized into the same group (if you want to see it that way).
That is also one of the main reasons I avoided creating my OC with a certain hairstyle. I feel like there are a lot of lesbian couples out there but the media/entertainment industry mainly uses 2 types of hairstyles. Super short hair or half their hair shaved....
I don't mind the hairstyles per se. I just get tired to see everyone think that in order to be a lesbian you have to look a certain way.
Having said that I think it is super important to investigate any topic you want to write about. Like cooking, science, etc.
As for romance I don't think people need to investigate much as long as they don't fall into stereotypes thinking that by being non-straight your romance will somehow be different. At least, that's how I see romance. All romances are equal but with slight difference from couple to couple.