Where can I find the page which guarantees me that any given version of any given package will be fully supported by a defined security team for security fixes for at least 2 years from release, preferably 3+?
That is my argument against using Gentoo. I have absolutely no idea how long any given piece of it will be supported. If you can point me to a resource which explains that, I might take another look.
I also have no interest in picking and choosing packages out of a bucket - I want a stable, well-defined OS that I can build on, and preferably one which is as close to what everyone else is using as possible so I can ask for help from people who understand my OS.
Yes, it might work out if you're running at scale, have specialised needs, and can dedicate resources to what essentially amounts to development of a forked distro. It doesn't work out for me, as I need to know that the system I'm building isn't going to be unsupported in a couple of months, and I need to know I can talk to someone who is running similar versions of everything I'm running if everything goes wrong.