Not the same person you're replying to. But I have some ideas to share.
> Another common claim I found to be false (in my case): "I learned so much configuring Gentoo!"
This isn't true for everyone. My general plan with anything is to follow the script exactly at the beginning. If that works out, start making incremental changes until something breaks or until you're satisfied. Gentoo taught me a lot of things that way - especially the kernel compilation (which is important to me anyway, due to my profession). Before this, it was Arch. And a regular Linux distro before that. All of them taught me something with the same strategy during the initial phase. Eventually the struggle gives way to familiarity and learning rate starts to fade.
> Well, no. I mostly followed the recipes like almost everybody else, setting flags and touching config files I didn't really understand
I don't know about anyone else, but Gentoo config files were the easiest for me to understand. I feel very much in control with them. The Gentoo wiki doesn't just give you recipes - they always tell you the exact reason for a configuration or flag (This is true for Arch as well). I have also created packages for myself - so I have a reasonable understanding of USE flags. I've been thinking about migrating away from Gentoo - but I like USE flags so much. Sometimes they allow you to access application features that are not available on other distros (because they have to choose build flags that suit the majority).
Something that helps me with this level of control over the configuration is that I maintain them as literate org-mode files with explanations and even diagrams at times. This might seem like too much work for a desktop system. And often that is true. But this workflow suits my interests and profession really well. In fact, at least 3 custom programs are part of my desktop - configuring Gentoo to my liking is the least difficult part in it.
> Ok, I'll bite: why is Gentoo best for you?
Finally. I said this in another comment. The most attractive part of Gentoo for me isn't the custom compiled kernel or software (I use flatpaks for most desktop apps). It's the package management system. Portage is by far the best system I've experienced for creating system packages.