What is the burden of proof in rebutting the presumption of diminished moral blameworthiness under s. 72(1)(a)?

In R v. P at para. 38, Mr. Justice Jenkins cited the following passage from R. v. A.O. as authority on the burden of proof borne by the Crown in rebutting the presumption of diminished moral blameworthiness under s. 72(1)(a): The youth court judge reasoned that in order to ensure that the most serious interventions are reserved for the most serious crimes, as mandated by the preamble to the YCJA, the burden of proof is not mere satisfaction, but rather "a very heavy onus to satisfy", as he put it. With respect, we would not describe the onus in those terms. Section 72(2) imposes an onus of satisfying the court, nothing more. However, in applying that onus, it is important that a youth justice court bear in mind the very serious consequences of an adult sentence for the young person, so as to only order an adult sentence when necessary to fulfil the objectives of the YCJA.