I’ve been using VimR the longest, which is a Mac-native GUI for Neovim: https://github.com/qvacua/vimr
Of course the vast majority of devs use whatever suits them, GUI or not.
And you couldn't have picked an editor with a worse GUI story.
ed is the standard text editor.
I say all that as an avid neovim user myself by the way. On mac/linux I use it through the terminal, on Windows I use it through the QT application.
WezTerm [1] is probably the best example right now but there are others.
These aren’t your father’s terminals.
The "lines" and other UI elements you see in those next generation terminals when you run TUI apps like neovim are still simple characters aligned next to each other to look like a line etc.
Stuff like GPU acceleration is only another layer which was put on top of all of that. At the core they're still using the same old technology.
So i'm really not sure the "layers upon layers" critique is well suited for terminals, in comparison with say some qt/gtk/electron/<your gui>. Also GP is mentioning emacs, which is mostly the same old cruft as a terminal emulator.
UI should be thought out at PRs and issues, but the same people who develop the main core. But they don't have to, because they're making a terminal application, which has its use cases.
But I so no reason why I should type my text in a terminal, when I can use a proper GUI application.
And I'm not even suggesting VSCode, even Emacs is better in this regard, which is what I use.