according to the spec, they are concerning CONTINUOUS drain current but not the peak current, the peak drain current is 1040A, of course it is restricted to its thermal condition.
And Rds(on) of the MOSFET would not have much change on the output current since it is quite small stuff compare with the others. it is just concerning the efficiency and its thermal. And we won't concern its Ids but just Vds, it will not damage the internal circuitry of the ESC as well. So as long as the MOSFET woudn't got so "HOT", it is sensibly OK.