It's not black and white at all.

This part is clear: "Pilot time that commences when an aircraft moves under its own power for the purpose of flight"

This part is not: "and ends when the aircraft comes to rest
after landing"

I think we all agree on when flight time starts.

But when does it end? Not clear at all...When you get to the gate? What about when you come to rest after taxiing clear but still waiting for taxi clearance? If you read the reg verbatim that's what it says...

The reg doesn't even cleary identify when flight time ends for a normal flight, much less a return-to-gate. In a return-to-gate the reg seems to give us a start time, but no ending.

The way you deal with FAR's like this is by going with the historical precedent, hopefully defined by something in writing from the FAA. In criminal law you could drive an A380 through a loophole this big....but in Admin Law ambiguities are almost always resolved in favor of whatever the agency in question desires. Many pilots have found this out the hard way by challenging FAR interpretation in front of the NTSB.