The reason you need a 9th man is not so much the stats, but to have a player good enough to get into the game IF NEEDED.
Our Wisconsin game, very clearly, showed we didn't have that this year. We played 6 players total in an OT game, with both Petro and Lee playing exactly 0 minutes. You just would prefer to not have that problem. (Without Keaton going nuclear, we had a 0% chance of winning that game. He did go nuclear, but we still lost due to horrific FT shooting and typical BIG officiating.)
Goode played in 28/33 games, which is 85%, so Zens hitting that mark would be more than ideal. Heck, 70% with 6 minutes per across those games would be great as well. But it needs to be better than Petro: 19/37 which is 51%.