If you use a standard package-manager-based taxonomy, there are five base distributions: Slackware, Debian, Red Hat/Fedora/CentOS (I’m unclear on which of those is currently the lowest rung), Arch, and Gentoo. There are also a handful of singletons, like Puppy and Void, which evolved independently (or from long-dead predecessors) but have no family to speak of. I think the only one of those that isn’t community-driven is Red Hat.
However, most base distributions are set up because their founder wants to try Something Completely Different, and that “something” is generally not user-friendliness. Even in Debian’s case, the core distro philosophy is about software licenses; its user-friendliness is almost a historical accident. Descendant distributions with a premise of “[distro], but user friendly” are not uncommon, though.