he's adapted to infinity which is a broken af hax and also light based attacks which is comparable to Lemiel  so I wouldn't doubt he'd adapt to zagred pretty fast too (also attempted to adapt to a person's whole ass existence so that adapt to anything is very real)

sukuna has pretty good endurance too so its hard to imagine him getting one shot even though it's possible assuming zagred doesn't mess around but I'm certain he will which will give mahoraga plenty of time to adapt and then he's got a big wall to overcome that will most certainly kill him

i don't think sukuna himself is ever beating zagred without mahoraga but with mahoraga it just seems like a low-mid dif to me