There are a lot of binary packages now, and explicit bin versions of big ones like firefox or the kernel. Without using those an update after some months may take half a day. With them, even a weak laptop only takes a few minutes.

Gentoo doesn’t want to push you into some compiled utopia, it’s offering you the option of customizing or taking control where needed.
You can have your system use binary packages but then set one packet to source, download the source, modify it, write a patch, and have a package with a completely custom sourcecode modification that you can easily keep updating as normal at the cost of it now taking longer due to compiling from source.