Honestly, about half of what I wrote was written last night when I was awake after an incredibly long day and half delirious, so I apologize if my arguments made no sense or caused offense, because my logic was pretty much shot by that point.
You'd never though about any of those issues? I've frequently considered them when thinking about Blitzball.
For example, my thoughts on buoyancy also solved the need for the Sphere Pool. See, normally, a large mass of water would increase pressure on the lower depths, and make objects of different mass and density behave differently. The purpose of suspending the water in an antigravity pool is to cancel this out, and maintain equal water density throughout the pool. Then, all you have to do is balance a Blitzball to have perfectly neutral buoyancy with the water, so that it will neither naturally climb nor sink when thrown or carried. Of course, Blitzballs then wouldn't float, as we see them doing in Kilika and Besaid, unless the water in the Sphere Pool was also less dense (and therefore, less resistant to movement) than water in a lake or ocean. Or the Blitzballs could be prepped for the Sphere Pool specifically, and different ones could be used for practice. Although, depending on how big a change that is, it might render practices night useless, as a Blitzball tuned to neutral buoyancy in water would normally handle very differently than one which floats like a volleyball.
I'm getting a bit off-topic, aren't I? I'm probably still not fully awake, my kitty decided it was time for me to get up, regardless of what I wanted.