Debian testing just isn’t a very good rolling release disto

What makes you say that?

It’s a dilemma; most Windows and Mac users would benefit from that kind of locked-down, idiot-proof format. Even having the choice of multiple repos is too much for them. So while I personally hate it, that’s what most people (i.e. non-Linux users) want and need.

I recommend Ubuntu as the beginner distro for everyone, but with the hope that they eventually drop the training wheels and switch to Debian.

It’s more than that. Ubuntu copies the Debian repos and then applies their own changes on top. Debian has a native (DEB) Firefox package, so Ubuntu specifically has to remove it for every new version.