I want to mention that you can exclusively use Official flatpak and distrobox and that is a much better security improvement than “Download this .deb and have it have root access on your computer!”.
Distrobox does not do any sandboxing, but it does prevent the repositories from running on your main system. I think that’s a benefit.
I won’t argue that it offers a clear advantage over traditional distroes (I personally hate traditiona distroes on the usability front, it’s only more usable because the Linux desktop is designed around that terrible way of doing things), but to argue it’s a step back for everything is unwarranted imo.