Not quite, I've corrected it. But yes, if you under-drive the MOSFETs the turn-on & turn-off times increase and so do the switching losses. It's easy to validate with a simulation. It sounds high but then those MOSFETs are switching 87.5A at 60v, 5250W, so ~1% isn't bad. A MOSFET with a lower gate charge would help, but at this level most have geometries that have that result.80W of heat???