I don't think you're asking the right question, Alsacs -- because we've had several guys who've been effective in the pivot who've gotten it done in a lot of different ways. Shot blocking is great, but it's the defense of last resort -- and often is a sign that the defense has broken down, but gets bailed out by the center [or another secondary defender] getting a block and erasing the breakdown.
Arinze wasn't a great shot blocker -- but he was massively strong and controlled the paint in that way.
Keita wasn't a great shot blocker -- but he excelled at positioning, knew where he was supposed to be out there, and called things out so that his teammates got in the right position most of the time, too.
IMO, the weakness of the zone THIS year is twofold: our forwards are too slow, and once they are out of position, they don't have the speed / length to recover. That's why teams that make the extra pass get wide open look after wide open look, and why we fall back on having Jesse fly out to challenge baseline threes. Benny Williams would give us an athlete with all of the right attributes for the zone, but his readiness has been low, and he hasn't gotten much PT.
The second factor is that we are weak up top, with two minus-defenders in the backcourt. Think about how disruptive MCW and Triche were, or even Gbjinje / Cooney. They made it much more difficult for teams to drive, pass, etc. because they were big, athletic, and had good anticipation.
Absent those two factors, the zone looks like the proverbial tavern league. And relies more than ever on the one plus defender we have -- Jesse -- to be superman in terms of blocking shots.