Instead of having to create a Collection Set, then individual Collections in that set, would it be possible to tell Lightroom to create a Collection Set, including all sub-folder and contents? This would save so much time if creating galleries etc. I am constantly doing this for a group of folders.
Sure it's possible and you should submit a formal feature request to Adobe about this
Just a little bit of my philosophy, based upon years of trying to understand the underlying design of Lightroom (and perhaps I am 100% wrong about this) ... the whole point of collections and collection sets is not to mirror existing folders, collections and collection sets are simply redundant and unnecessary if you want to mirror existing folders, you can just use folders. So I honestly don't see Adobe spending time on this at all.
That is not true of the Web tab, the Templates for creating Galleries cannot use the Folders only Collections.