The drive has a WAY to low gearratio.
Better using higher KV motors and a gearratio of 20-1 or so.

Even Bosch 750's struggled with a 5-1 gearratio to 250mm wheels.

And if you think speed is a problem.
Bullfrog uses a 20-1 gearratio and 250mm Full foam wheels, with 170 KV 120mm diameter motors on 10S.