You can hand load almost anything as hot as your heart desires. Look at the factory loadings that what I would go with. Not the assumption that you just posted
How confident do you feel about convincing a judge that "capable of" means "there are factory loads for it", and doesn't actually means "capable of"? Keep in mind that you could fall on the same judges that have decided that some SA lower are indeed full-auto lower, on the basis that all you need to modify them is a machine shop.
Even if somehow, you end up with a very lenient judge who accepts that the limit on the energy is "factory loading" (won't happen, but let's suppose for the sake of arguing), how confident are you that no factory will do like buffalo bore does with the 44magnum and 357 magnum rounds are start producing factory heavy loads? To push a 9.6kj projectile up to 10kj, it's only a 4% difference. On velocity, it's a 2% difference. 10kj is actually in the margin of error of a 9.6kj ammunition.
As for "You can hand load almost anything as hot as your heart desires", it is more or less true. The physical limit is the cartridge capacity. You need about 3.3 square cm of capacity to produce 10kj of energy. So going by theory alone, any cartridge with that capacity is "capable of discharging a projectile with a muzzle energy greater than 10,000 joules". To give you an idea, a 308Win case has a capacity of 3.6 sq cm.
So are 308Win prohibited? Probably not, as some energy is lost during the process that transform the potential energy in the powder to kinetic energy in the bullet. But I have no doubt that right now, someone could do jail time for a 338Lapua magnum or larger.
The words "capable of" encompasses a lot. And there's a principle in law: "The legislator doesn't mean anything it doesn't say and doesn't say anything it doesn't mean". After looking at the laws and the facts, a crown prosecutor should feel confident to go ahead with charges if someone sells, transport or use a 338LM, so you can imagine how a 375enabler isn't even a question.