Jefferson has better reach, standing vert and consequently about 3" no step vert reach on Kanter, at least coming out he did.
https://www.draftexpress.com/nba-pre-draft-measurements/?year=All&sort2=DESC&draft=0&pos=5&source=All&sort=11
Maybe after that knee injury it's closer but I doubt it. Jefferson has a very good ability to quickly get a hand pretty high up. Not to mention before multiple hijacks the OP was about AJ's supposed improved basketball body.
Kanter's measurables are not his strongest suit. If he ends up a better defender than Al it won't be because of what he was born with.
Derrick Favors of course is in orbit above both of these guys and on the moon compared to Sap, comparable to Howard, McGee and Okafor.
I don't know about the offense but i am 100% sure Kanter will be a better defender than him