Another inaccurate assumption is that the rotors are the same strength. 25.5 ROAR rotors are weaker than the rest of the spec range, and mod rotors are even stronger again.

So would that make the mod have stronger brakes?

Yes.

Yet here in the US we have mod guys baking their rotors to make them weaker. I don't have any experience with that, or know the reason for doing it.

My guess would be to take the edge off the punch and get higher RPMs. Though they could just put a stock rotor in instead of baking them.

That's true of any permanent-magnet DC motor. The term is "dynamic braking"; the braking force is proportional to the speed of the motor. If the motor isn't moving, braking torque is zero. The only remaining opposition to movement would be provided by the cogging force of the magnets, and the friction of the bearings and brushes (for a brushed motor).

We had the same problem when racing on a sloped parking lot. Using a LeMans-style start, with the cars against one wall and facing across the track, solved the problem. It also made it much more difficult to get a hole-shot!