How high do you actually need to get in the NBA? A shorter player, or one who lives by attacking the rim, probably needs more vertical. But, if we're talking shot blocking, I could actually see a poor vertical being a pretty minimal consideration for a 7 footer. Relying less on leaping and more on timing and positioning might lead to just as good shot blocking. The game isn't played at 15 feet, and Bender, between height, reach, and vertical can get as high as NBA players really need to get.
So, it doesn't seem like raw vertical actually measures something overly meaningful for a player of his height. What we might care more about is how quickly he gets off the ground. (Think the NBA equivalent of a catcher pop time.) Of course, we don't have that number, but that's a better measure of real game explosiveness, I'd guess, than vertical. Also, as others have pointed out, he's supposed to have great lateral quickness. What I don't think others have mentioned is that this can make up for poor leaping as well as adding perimeter versatility. A lot of the need for elite leaping is about being out of position and recovering through the air. Great lateral quickness could allow a shot blocker to get to the spot where they need to be to go straight up instead of diagonally. That alone should make up for any deficiency in vertical in a lot of situations.
Anyway, from what I can tell, barring a trade, Bender sounds like the best pick. Getting someone who could be a star is far more valuable than getting someone who can be a rotation player right away. Dunn and Hield don't interest me for this reason. I don't see them having sufficient ceilings. Murray and Brown are more interesting. This team is really fun to watch, but it's probably two elite players from being a title contender. Using a number three pick on anyone without that upside would be a huge waste of resource.