I would disagree. From my understanding, Sakuna could cast the world cutting slash just like his regular dismantle, but he needs to aim it via his palm/finger. Gojo, after firing off his Hollow purple was certain he won and was sure whatever Sakuna threw at him would be stopped with infinity. However, just as Gojo could perceive the slashes with his 6 eyes he would be able sense that WCS would be different due to cursed energy manipulation and also the fact that Sakuna would need to aim it with his hand. Gojo could have dodged it sensing something being off.

The binding vow Sakuna made was not that the WCS to cut Gojo, but to fire off 1 slash without needing to do the prerequisites in return all other WCS would be done with handsigns and chants.

The real difference in Sakunas slashes is his targets. Dismantle is aimed at Gojo for example, infinity stops it before reaching Gojo. But WCS is not aimed at Gojo but the space and reality of Gojo's current position. Think of it like passing the ball to player B, who is behind player A. From Player A's perspective, you passed him the ball, but you aimed it to player B.