There can cooperatively be multiple implementations that have different developers (as long as they coordinate with other implementations), and written in different code , different languages, and with different features that don't break consensus.
Which won't happen if one group (such as Bitcoin Classic) decides that the other group (Bitcoin Core) are not the right people to be doing the job (which is exactly what is going on).
Gavin could fix all of this by simply making a statement that he won't disagree with the Bitcoin Core group (but of course he won't ever make such a statement so we have a stalemate).
Yes, but to be fair to Gavin , he has expressed and is contributing, somewhat, across different implementations. Additionally, he is treading a grey line of simultaneously assisting a coup and not taking a leadership role. If anything he appears not to want control or the responsibility it demands , but wants to do whatever it takes to steer bitcoin for more capacity. I think, unlike Hearn(whose politics are antithetical to bitcoins principles) he is sincere and genuinely believe that bitcoin will be more decentralized and secure if it can grow rapidly and the best way to accomplish that is increase maxBlockSize. There is some validity to this line of reasoning but I still cannot find any reasonable benefit to choose Classic over Core+ Segwit when studying the facts.