Momoshiro used it. Are you saying he is a 10baller?
Oni's ten ball move is likely what he used to dispatch Kaji.
So like I said. BJK can't be a move specifically for a 10baller.
It's clear that the same move used by different guys have different results as a function of their base stats. Momoshiro is not a 10 baller but he can still use a move that a 10 baller can, with lesser effect. Given Oni is obviously much stronger than Momoshiro it's safe to assume no one in the G11-G20 can return that. I consider that to be an appropriate power level for a 10-baller.
But then since I'm pretty sure any 10-baller can crush a G11-20 without using any special moves, this means BJK is likely a weak move at the 10-baller tier.
So given the serialized information I'd say Ryoma is stronger. The revised Kaji vs Oni game significantly boosted Oni's power. Before it looked like Kaji was just random court 3 level guy they grabbed to fill Oni's spot, but in the volume it's implied he can return BJK (he lost to a BJK+ level attack) and yet Oni still totally crushed him.
It should be pretty clear Oni is one of the major characters in NPOT. He told Duke to only use 60% against a middle schooler, which implies he thinks 60% of his power is sufficient even though Duke believes using 60% of his full power might result in him losing the game. That said he really hasn't done anything really impressive so far, which is why he supposed to have an upgrade in the volumes. I don't have the latest volume so I can't say for sure, but the scans looks legit.