Most of your suggestions feel too fanservice-y rather than actual legitimate candidates. Half of your suggestions are enemies or former enemies. I feel like that would reflect poorly on LGBT+ relationships rather than be good representation. These are popular ships, rather than legitimate suggestions with any story beats or reason backing them up. I know that characters don't need a strict "reason" to be gay, but I think injecting romance into any of these stories, gay or straight, would be detrimental and/or pandering, rather than natural story beats.
Most Champions aren't involved in romantic relationships, so its entirely possible that some of them ARE LGBT+ but its not relevant to their story, so it isn't mentioned. I think stories can be just as strong with platonic relationships anyways. People can just be close friends, too.
Also Neeko was confirmed to be more attracted to girls than guys. She's probably the most organic representation we have. Doesn't feel tacked on to an existing Champ, she just is attracted more to women.