It works within the leading actor and leading actress context. There is no non-binary category. IDK what the gender rules are for applying to one or the other, but there really only should be one you can apply for as an actor. I am pretty sure Redmayne would be in the best actor category if he was good enough to be nominated. So in conclusion, it works fine. Your one in a million scenarios dont even break it. Your issue is no longer with the actor-supporting actor distinction but that there arent a million different gender categories to satisfy your ego. If someone is a co-lead, there is no #1,2, and 3.
Your own ideas for co-leads don't even work as noted here. Can you have ten co leads? How do you determine who a co lead is? At what point is a co-lead a supporting? Your feelings? Your arbitrary distinction of what is and what is not a co-lead? Starting off with a non-binary argument really shows you have nothing here.