Bare vi does not have windows, visual selection mode, multiple level undo, color schemes, etc.
NVim wants to improve some defaults, which cannot be done if it is beholden to all legacy code. That being said, I still think this specific undo example is insane.
Vanilla Vim added it in 2016 I think, but by that time I had already fully switched to NeoVim and it didn't seem worth it to me to switch.
That fell apart when people wanted vim to do some more modern IDE kind of things like all the “… on save” stuff (build on save, test, lint, etc). I think LSP support is native in neovim as well.
I believe vim merged asynchronous plugin support a while back though, so I’m not sure how different they really are anymore.
Just run make from another terminal...
I often use vim or nvim on disposable machines, so persistent undo is something very low on my list of things I want.
As far as really cool uses for tree-sitter go, ast-grep is a fantastic tool. Of course it's a standalone program, so it doesn't need nvim to make use of it.