The Brummbar has decent speed, especially if you consider that it still is a good HP/high armor unit. Only it's rotation is lacking but for turretless vehicles still one of the best.
yes but as you said no turret, and also slow manual aim time and reload and 35 range,
it needs to move in and out faster than ATG and 60TD with twice its range.
and i believe brumbar needs to be stationary for its rounds to land near where you click