They’re really not. Stability matters, but a wm has very little to do with actual rendering, it’s more placement, title bar and decorations, emacs as slow as it

They’re really not. Stability matters, but a wm has very little to do with actual rendering, it’s more placement, title bar and decorations, emacs as slow as it can be would be perfectly fine unless you have some crazy extensions on top, hence running two instances.