It feels like /opt 's official meaning is completely lost on developers/packagers (depending on who's at fault), every single directory in my /opt belongs to standalone software that should just be put into either /usr/lib or /usr/share with some symlinks or scripts into /usr/bin.
No, they have it right. Add-on software means “added to this node/machine”, as in not part of the system image used to configure multiple machines. It’s all very archaic.