Here's an interesting aside: I downloaded and installed the free version of
Luminar 3. When I went to install it, the default path was shown as /System/Applications. I changed that to /Applications; I had not even known that /System had an Applications folder!
I don't know what would have happened if I had used the default, but I don't want to allow a third-party app to be in /System, nor modify /System in any way.