I'm also a long-time desktop Linux user. Since 2003. I'd say that my average linux desktop computer has about half and half repo and non-repo software. I can't imagine limiting myself to just what was in the repos. There's only a tiny fraction of software in those even including personal repos like ubuntu's PPA system.
With Arch / AUR even non-repo software feels like repo software.
However, on my ubuntu installs lately, I've found myself having to go with non-repo software for things that are in the repos. Because the repo version is just so far out of date. Version freezes with only security updates means lots of old software. I was loading my Arch configs on ubuntu and things were breaking. Update to current stable version and suddenly things work again. If i was stuck with repos, I would have just not used ubuntu at all.
I have a few applications which are installed from source, and as you say a couple of things installed beneath /opt. Currently that is: Firefox, golang, Arduino studio and Calibre.
