> Even if true, technical people can work around this by either spoofing a non-external drive or using `ln`, no?

IIRC Google Drive for Desktop won't sync the target of a symbolic link. It will sync the target of a hard link, but hard links can only target the same filesystem that the link is on, so you can't target an external drive on macOS AFAIK.

I can't speak for the other software you mentioned.