True, but even then the efficiency is not that bad. 70% or so, very close to a regular flyback.
Adding insult to injury, the SN6501 uses R_DS_ON(temperature) to balance the flux. But at that power level any dishonourable trick is acceptable. For example, a series of 100mW flybacks I use in quantity for gate driving purposes are based on a 6mm OD ungapped toroid. There are enough volt-seconds available that allow me not to care. It is super-tiny and reliable, f^Hignore the rules.
Best regards, Piotr