as far as QF is concerned, you purchased a full J class fare from MEL-SYD, they delivered you to SYD domestic airport with all of your luggage.

That's the end of the contract.

Whatever you have done with Thai is your own choice. QF does not need to take that into consideration.

If anything TG should organise a premium transfer service for their full fee paying premium customers. this is none of QF's concern.