To state some blatantly obvious facts, people do open source on their own time, they have limited such time and many commitments, and they explicitly allow forks like neovim for the aspects they can't find time for. Vim and neovim have chosen very different design constraints, and there's no reason why they can't continue to exchange code where it makes sense. Putting one of the two down seems unproductive.
The leaders of large projects like Neovim are seldom critical of the competition, and when they express criticism it is measured and proportionate. We should all learn from them.
(Your OP here is still quite useful. Thanks for putting it together.)