I recently switched to gnome-web (epiphany) from qutebrowser because it has gotten better in the past months. If a page makes the browser slow, I blame the webpage. In most cases, I can avoid the shitty webpage.
But still, I hope it catches up for the instances I have no choice and open a different browser for a specific webpage.
This is so wrong. Especially the assumption that almost no one would want to have more than 1 DE installed.
Most DEs have their own configuration which don't conflict.
If the maintainer of a distribution has their shit together library incompatibility is no issue. Even on Gentoo you have to ignore everything portage is trying to tell you before you get in trouble.
In the past I even ran two DEs at the same time, sort of. You could start an xfce-panel while using enlightment or good old classic windowmaker.
Later I used Gnome and running my own fork of dwm in a nested Xserver. With wayland this option hasn't gone thanks to Xwayland.
If systemd is correctly set up for it, you get a different seat for every DE, no matter if some seats are hosting the same DE or a different one. I am not sure what will happen if you have several graphical logins with the same user, never tried it.