[Chris is me]

All of the below assumes a roughly centered CG and even tractioned wheels (all roughtop or wedgetop or kit)

With four equal and high traction wheels on the robot in the long orientation, turning on a dime is basically impossible. It can be done with large wheels and a lot of "jumping", but it's close enough to impossible that the robot's basically worthless.

Adding another set of wheels with no drop fixes this a little bit, but generally not enough without some specialization. 25's drivetrain is an exception due to a lot of subtle reasons I don't really want to go into here.

Dropping the center wheel means that effectively you have shortened your wheelbase by half, since only 4 are on the ground. This makes your wheelbase wider than it is long so you can turn just fine. As a bonus, when you're pushed on one side it's very easy for the robot to "lean" on those wheels to make you harder to spin than, say, the same drivetrain with omni wheels, leading to great pushing resistance.

With a 6 wheel no drop omnis, you get comparable performance and even better turning at the cost of being more easily spun yourself. 4 wheels with 2 traction and 2 omnis exaggerate this effect further. 6 wheel drop is basically the very best of most worlds, for most games.

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In the case of a wide body robot, Lunacy demonstrated you don't _need_ 6 wheels to turn well.