Doesn't "... seem he was ..." - he was!
You ask " ... the norm to have been transferred between prison hulks ...". Being transferred to a Hulk, preparatory to boarding a convict ship was the norm - not transferring between Hulks.
George Smith first appears on the Leviathan's books for the Quarter 1 Jan 1826 to 31 March 1826, Portsmouth Harbour, having arrived from his sentencing in Lewes 19 Dec 1825 (cannot determine exact date of arrival). During that quarter no prisoner was transferred to a convict ship. Some died, some were discharged to a different Hulk, some freed on pardon and some freed having served out their 7 years while awaiting transportation.
The quarter that recorded George's transfer to the Marquis of Hastings (9 Apr 1827) saw 130 prisoners transferred, many of whom had been waiting over a year (to either the Marquis or the Layton).
The Marquis had sailed from London and was carrying a detachment of soldiers. Finally, the off!
The Sun (London) 19 April 1827
SHIPPING INTELLIGENCE (this day)
Portsmouth, April 18 - Wind N.W - Sailed the Marquis of Hastings, Drake, for New South Wales