George McDonald
Not to despair, there are solutions to the 3 points raised. I am sure one day the good folks at Microsoft will make it easier.
1) Correct about the move function, though following instructions in my post above, it is possible to copy a form back to yourself.
2) Scroll to the bottom of the list and pick "Enter custom value". The value you want is GUID from Form URL after the 'id='. The same Form ID is needed in the 'Get response details' action.
3) Hope step 2 resolves this, otherwise post a few more details.
RE: "can someone explain what it is we gain again"
Some of the benefits I have found is:
a) Group ownership of the form. Helps with staff movements.
b) If form has questions relating to upload of files, the file now land in the groups SharePoint folder: Documents > Apps > Microsoft Forms > <form name>
c) Default Response spreadsheet when accessed for the first time in Forms, land in the groups SharePoint folder: Documents > General