Emacs has a very long tail indeed of elisp extensions which Neovim has yet to fully catch up with. Neovim is well on its way however, and uses a programming language which many people already know and which is in any case familiar and easy to pick up. Lua has its quirks, elisp is pretty weird even for a Lisp (credit where credit is due, the elisp documentation is fantastic).
I've used Emacs off and on for years, and lately have settled on Neovim. The Spacemacs / Doom style configuration gives Emacs a fairly nice user interface, but I've never managed to hit a sweet spot of running all the fancy stuff I want to run, and not having the editor randomly pause / stutter.
With Neovim I've found that I can load it up and it still starts in under half a second, keeps up with typing/scrolling under all circumstances, and so on. For me that's the right tradeoff, ymmv.
I’m under the impression emacs performance will improve but agree it’s an issue, particularly on very long lines - my understanding is that any modes must recalculate things (font colors, etc) on every change and recalculate major parts of the file. Iirc emacs 30 implements treesitter and a few other things which should improve performance, but some issues still undoubtedly remain.
Edit: and I really do wish there was more unbiased content relating to the pros and cons of either.