Most of these tools you mention are designed to work best as an overlay to your $HOME. toolbx, distrobox, and to some extent flatpak and snap. NSL is built to give you the "pet" virtual machines with limited integration to the host - you can get to the host filesystem if you want, and you can use the host's Wayland session. I think a better comparison would be using NSL instead of using a remote computer or VM.