Since Linux has no concept of a base system, it's a stand-alone kernel with a hodgepodge of crap around it - this distinction makes no sense on Linux.
/opt is generally for software distros for which you don't have source; only binaries. Like commercial software packages. More common on Real UNIX(R) because most Linux users outside enterprise aren't running commercial software. You're putting your $500k EDA software under /opt.
See, you assume here that /usr/local/ makes any sense.
I use a versioned appdir prefix approach similar to GoboLinux. So for me, /usr/local never ever made any sense at all. Why should I adhere to it? I have ruby under e. g. /Programs/Ruby/4.0.0/. It would not matter in the slightest WHO would compile it, but IF I were to need to store that information, I would put that information under that directory too, perhaps in a file such as environment.md or some other file; and perhaps additionally into a global database if it were important to distinguish (but it is not). The problem here is that you do not challenge the notion whether /usr/local/ would make any sense to begin with.
> /opt is generally for software distros for which you don't have source; only binaries.
Makes no sense. It seems to be about as logical as the FHS "standard". Why would I need to use /opt/? If I install libreoffice or google chrome there under /opt, I can as well install it under e. g. /Programs/ or whatever hierarchy I use for versioned appdirs. Which I actually do. So why would I need /opt/ again?
You’re presenting your comment as a rebuttal but you’re actually arguing something completely different to the OP.
They’re talking about UNIX convention from a historic perspective. Whereas you’re talking about your own opinions about what would make sense if we were to design the file system hierarchy today.
I don’t disagree with your general points, but it also doesn’t mean that the OP is incorrect either.