I think it's difficult to practice airshotting in any way that'd make sense. Airshotting bots might help in the long run, but as noted, they're predictable to a degree in every case imaginable. I personally just juggle bots during downtime when I've got nothing else to do.
If you want on-demand practice, I'd say stick to pugs and MGE/DM. You're gonna be closer to a realistic situation in which you might have airshot opportunities, without 'risking' a team practice or official match.
MGE granary/spire does seem like the best option if you find someone of equal skill to spar with. I absolutely loathe mge with randoms due to the whole dick measuring aspect to it, and people who try way too hard.