It seems an unfair thing to say until you experience it, or your loved one does. My SO uses gnome-ubuntu, and I am at a loss to explain why firefox crashes multiple times a week on her PC. On my gentoo box? I think the browser hasn't crashed randomly in...months? And I am on ~arch at least for firefox so they are the same version afaik.
Gentoo doesn't have as many devoted, paid testers from what I understand as Canonical does, so how is their stability relatively worse?