I agree that the defense last night was the best part of the game - we sustained it for 4 quarters, just about every possession, and there were no long stretches of absentmindedness, failed gambles or any other nonsense. Kornet was a big part of that.
But I noticed that when Embiid was on the floor, Grant Williams was usually the primary defender on him (sometimes Griffin), and Kornet was guarding the 4 and only coming in to help on rebounds and such. The block on Embiid was awesome, but Kornet was not assigned to try to keep Embiid out of the paint - and a damn good thing. What makes him look athletic at 7'2", moving fluidly, is his lack of bulk - he simply doesn't weigh what a lot of other players his height weigh, so he can move more on one or two steps. But that also means that Embiid would flatten him like Wile E Coyote.
On the other hand, when Embiid sat and it was Harrell was out there at C, Kornet covered him, and basically stunted on him. Was in position for some good rebounds, out-maneuvered him on both ends of the floor, made some great passes. It's clear that Mazzulla understands the situations that Kornet is good at, and doesn't ask him to do things he can't do (no matter what his height is). There are a lot of teams against whom he can very adequately spell TimeLord even in the playoffs and if he can put forward the effort we saw last night, he will be a big positive out there. And for the handful of players in the league who are just too much of a load for him to cover in the post, we clearly have a plan.