I've never had logging in with a different desktop environment cause problems. (And I wouldn't expect to. The desktop session selector on the login screen is there for a reason, after all.) Your comment makes me wonder what desktops you tried that stepped on each other, and what bugs you're referring to.
In any case, if I had an experience like what you describe, I would simply re-create my user account and its home directory. Going through a whole OS install as you suggest would burn a lot more time with no advantage, which doesn't seem "better" to me. To each their own, I guess.
Remember as well that your "distro spin" approach is only possible if such a spin exists. Example: If someone wants Linux Mint for its beginner-friendly community support, but also wants to try KDE Plasma, they can. But they're going to have to install Plasma after the base OS, and switch.
Sorry you had bad luck there.
I guess that's one way to be sure, but to me it seems excessively limiting. I have switched desktops on Debian-based distros, and the only tidying up I remember being needed was removal of the old desktop's packages (to de-clutter my application menus) and a reboot (to launch the new display manager).
My recommendation to a new user would be to try whatever distro/desktop combo is appealing, and if it doesn't work out, either do some troubleshooting or just move on to another one. It might not be a path as well tread as the distro's default, but it might work fine. You'll never know if you don't try.
That's untrue in at least some cases. Of course, different distros have different policies and people maintaining their desktop packages, so YMMV.