Yes, underneath they are all using a Linux kernel, but the user experience between Gentoo and Mint is radically different. And Fedora is a very different experience from Arch. Or Ubuntu vs Void.
I've recommended Zorin to my dad. I would not recommend Slackware to him.
It's easy to say that Debian-Fedora-Arch are all Linux, but between all of their derivatives and all of the independent distros, there is a vast array of user experiences available.
Why does Grant have a moustache