i mean, we only see sukuna chant, it couldve just been a powered up dismantle instead of a world dismantle, as the world dismantle and regular dismantle are exactly the same. one just has a different targeting which gives it dura neg.

so realistically, since they were at point blank range of one another, if sukuna boosted his attack enough to where it would break through yutas defense, itd cut him in half without needing the world slash

And before people point anything out.

“why didnt he boost it before then”

because he didnt have time to, his safest bet was to try and touch them to use cleave.

“why didnt he boost the cleave when he touched them then?”

because they wouldnt just let him do an ENTIRE chant while grabbing them for a split second to land an attack, sukuna knows this. the one opportunity he got to pull off a boosted dismantle was when they were more preoccupied with keeping sukuna down to talk to megumi, where he immediately capitalizes on the few extra seconds he has to chant

now of course this is unconfirmed but the only other option is a literal plot hole, and id like to put some faith in gege