I have heard Norman play it many many times and the key is the groove, not the notes. He plays it different every time but has some of the best groove ever. Heard him play with Wilco on one of his farewell tours and just playing one repeated note for the intro of Roxette while Wilco talked to the crown knocks you sideways..... genius player and one of many favorites of mine.
I love slap, I was a huge Mark King fan back in the day and went from that to Stanley Clarke, Larry Graham, Marcus Miller and up to Victor Wooten the alleged inventor of double thumbing. The technique is irrelevant, it must contribute to the music and many forget that. They have all been guilty of indulgence IMO but they are all more than capable of letting the music speak.