“compile pretty much every command your distro has in exchange for a measly half a second faster boot times!”
I don't deny the existence of people with such motivations, but I'd argue the sheer amount of freedom that Gentoo allows is its defining feature. And for that, even though I don't use it on my main device, I'd argue it's actually one of the primary contenders for best distro.
It's probably related to installing packages through the AUR, even though it's known to be unsupported on Manjaro specifically due to their policy of holding back packages.