10A^2*0.014=14W dissipated in the FET for the on-time.
Multiply by FET's "on" duty cycle for rough conduction
loss power. This is where Ron affects heat. Power rating
involves Ron on the input side, package, heatsink thermal
attributes and supplied airflow on the exit side. It matters
little if you have a 1oC/W or a 2oC/W thetaJC package if
you put in onto a inadequate heat sink or feed it still air.
Less Ron is better until it costs you something, like more
switching losses than you shed conduction loss by the move.
Typically you gain (lower) Ron by die area or lower BVdss,
your two handles on the drift region resistance.