When the competition was being run for the JP replacement, a certain large manufacturer in Lancashire worked with an ex-QFI retired 2* as its consultant when developing their proposal. As airframe and especially engine efficiency had advanced a tad since the JP1, things were clearly going to be a bit easier when it came to meeting the spec. JP and Vampire T11 both side-by-side, so let's go with that. And we can do an hour on half the fuel, so let's halve the fuel capacity!
As others have noted, PC9 was a clear winner apart from the unfortunate part about it not coming from Brazil.