The reason why the focus was on Enma was probably due plot reasons I think. It makes sense Oda wanted to show Enma in high regard.
Besides we presented arguments for why Enma is a training tool that empowers an individual via training since when Oden died his arm was normal, no haki was imbued in the sword.
As for the ACoC matter, there's no evidence ACoC can't work performing more than a "one point target" and not many, besides it seems it works very similarly to ACoA pattern wise.
He did it with Pica as well btw. A 3 swords attack only channeled in one point.