Not just the JP but all comps and muzzle breaks are banned in NRA High Power and NRA High Power Sporting matches. It because of the firing line points are 6' wide, not because one is better than another. NRA HP Rule 3.16.1 Is there an organization that banned it because they felt it was better?
IMHO a lot of time and ammo has been spent researching comps and although they do fulfill a purpose increasing accuracy is usually not one of those benefits. When group sizes shrink using a comp it is usually because the shooter is more relaxed not that the gun is shooting better.