From your class/weapon bans and the map shape I would have thought that it'd be extremely difficult to make kritz effective by getting multiple picks as anyone can jump anywhere and there are no chokepoints. But I didn't play.
When you say ubers build in no time, do you mean that the build speed is altered?
Medic has the strongest throw? that's not what is said on jaguar's nerds video
That needles thing is a real bummer, but yeah you can't alter the game behavior sadly. I think having plasma like projectiles is always nice.
Why don't you ban the loose cannon following the same argument then? Like stickies it's really easy to make an explosion det in the air and hit the ball.
One last question : I understand you want this gamemode to reward mechanics, would you say it's only that or is there team decisions to make like in 6s?