Is there a way, another fora than arbcom, where the community can discuss this issue - decide how we'll use the word "founder" and settle it for good?
Yes, RFC, but you say you've already tried that. RFC's don't really work unless the people involved are willing to listen to the comments, and it sounds like some aren't.
I don't really see how there can be any reasonable arguments for any position other than simply describing it as disputed. Wikipedia does not exist to settle disputes, we don't decide who is right in an argument, we just report on the argument.