By "trying hard to be polite", I mean he was making an effort to be polite when he had no need to be after Bram was already rude and dismissive, not that Thiago has trouble being polite. Read the neovim issues in github: Thiago is a model of good-natured engagement with almost everyone. In the original patch request thread he's far from impolite, and he's more polite than Bram is.

And "makes debugging difficult" is an observation, not a criticism or valid reason to reject--it's certainly not detailed, as you said. Yes, it's more difficult debugging it directly, but the architectural separation makes the components more loosely coupled and more easily tested in isolation--it's a valid tradeoff, and one the neovim has demonstrated to work well in actual fact.

I mean, it's an accomplishment for Bram to add async to vim, but let's not forget who actually did it first, successfully, and along the way accomplished a lot more.

Why are you so hostile to neovim? By any measure they've done a tremendous job modernizing the codebase for vim and rejuvenating development of both neovim and vim.

Step back and ask yourself: if you were approaching both projects fresh, and asking which you might want to participate in, which would you choose and why, ignoring politeness on either side?