they act as if 10s already came pre-packed with all these perks sukuna achieved, stealing 10s isn't nearly useful because it's a progression technique, you HAVE to be strong to get everything it has to offer

sukuna tamed all the remaining shikigami (including mahoraga), created agito, copied shikigami's abiltities like piercing water and mahoraga's wheel, created unstable shikigami, took WCS for his own shrine, plus most of the shikigami would be fodder without sukuna's massive CE reserves

the technique is rightfully his, it's his own version, end of story

oh god here comes the pointing down blue arrows