Bryant and Williams pretty much have the same measurements. Both are about 6'10" with huge wingspans 7'6". The difference is the athleticism. Williams is an elite athlete who is similar to a Shawn Kemp in that regard. He is very fluid, quick, and has anywhere from a 40" to 44"(44 is unlikely but that is what some at Texas A&M said they once measured him) vertical leap. That is why he is expected to be an elite defender and shot blocker in the NBA. He has the foot speed and agility to defend anyone. He has already shown he can be dominant in the pick n roll as well as lob plays. He doesn't have any real mid range game and is a terrible ft shooter. But he can help the Celtics right now as a defender and with lobs and pick n rolls.
Bryant had a more modest 32" vert which might explain why he didn't block that many shots in Indiana with that wingspan. He is not a good athlete and doesn't have a good feel for the game. He does have a decent shot now but he would be a non-factor in any offense. He really only offers an elite wingspan. He is a project that will likely spend a lot more time in the G League.