Not sure I agree that Gentoo shouldn't support all options. Sure, it can only support the options that people are willing to put the work in for, but as long as people are willing to do it that's what Gentoo is all about.
If Gentoo isn't about choice, then what good is it?
By your own argument, there are a bunch of vertically-integrated distros that do one or two things really well. I think that niche is already well-covered. Why try to out-Ubuntu Ubuntu?
The whole point of a distro like Gentoo (and to a somewhat lesser degree Debian) is to be all things to all people. For those who need a distro that is all things to all people, they're the best choice. THAT is their niche that provides the polished user experience (if you can call a lack of polish, polish).
I agree that the lists can get a bit curmudgeonish at times, and I filter that out. What is important is to support a reasonable set of options.
Personally I like the generic distro. It allows me to have a moderately consistent experience across everything from a desktop to a server to a diskless set-top box. Sure, there are niche solutions that might be closer out-of-the-box for each of those, but then I have to keep on top of multiple distros all moving in different directions, and heaven forbid the client on my desktop or set-top box is not compatible with the server component on my server.
My biggest concern with the vertical-integration trend is fragmentation. Hopefully with everybody working on their own init+X11+DE and who knows what else we don't just all end up with suboptimal experiences, since nothing is shared but maybe glibc (but not gtk vs qt!).