I used to be a gentoo user in the 00s. Recently came bsck to linux and I find tge popularity of gentoo died down as fast as arch became popular.
Why does arch exist ? Is it like, gentoo but with a binary cache ? Can you automatically build everything from source still ? Is there something equivalent to use flags .
It's a rolling release with minimal changes to packages from upstream, and generally the latest versions of available software in the repos. I guess you could go through and rebuild the whole system from source if you were determined to, but a quick look at the ABS wiki page doesn't make it seem like it's set up to make doing so all that easy. For other software not in the repos, the AUR makes it easy enough to build them from source, though there's often binary options available as well. The base install is pretty simple, so you can build upon it as you'd like if you really want to go wild on a minimal, highly customized system. Or you can go wild installing what you'd like and trying all the things.
You can set general options for all compilations in /etc/makepkg.conf, and package specific options would probably be best handled by just downloading a PKGBUILD for the package in question and editing it to include the option you want to enable. makepkg won't ask you about options by default when building something, but it's not that complicated to edit the PKGBUILD prior to calling makepkg.