Regarding his offer to bring them back early, I can't think of any other reason for that other than for political points. It really wouldn't make sense to spend the money and time on another dragon especially when they could just have the astronauts become part of the next crew rotation.

Crew-8 is on SpaceX's Crew Dragon. NASA has been using it for ISS crew rotations for several years now (Starliner was supposed to be NASA branching out to not have to rely on only one company for that)

They were moved to the Crew-8 mission months ago and the vehicle that will bring them back has been docked to the ISS since September

All orbital rockets (with only a few exceptions) are expended into the ocean once used, with starship this is only temporary while they improve the design