I would say that all your points just go to show that they make great BFFs not a romantic relationship. Heck, in S2 Ruby called out their "ship" names as attack strats. Not that I'm against same sex relationships, I think making Yang into girls makes total sense. But Monty built a wonderful relationship between Blake and Sun, he cares about her a lot and she likes how he cares. It's because of his dedication to her she was able to open herself up to people. Also, just because the voice actors are into it, or because theres a lot of fanfic, doesnt mean it should be canon. I'm sure Michael and Lindsay want Sun and Ruby to get together because they're married in real life but that doesnt make sense for the show.
But the biggest reason I'm just not into it is because it feels like their relationship was established late. If you go back and watch season 1 to 3, the only time they really connect is when Yang relates searching for her mom to Blake searching for Torchwick. Other than that you dont see any personal connection until season 5 where Yang, out of nowhere, is upset that Blake "just left them" and now they hold hands to fight Adam. Couple? I think not.
This is just my own opinion, but I think it better fits Monty's legacy to finish a romantic connection he established. I ship Blake x Sun and for Yang I hope she finds a nice girl. Either Yang x Coco or give Yang a nice Atlas girl.