interesting point
second segment climb is really important if you have an engine failure.
and there are some times where there are so many obstacles nearby you would want to know the performance
BUT, I think most of us would take off and not retract the gear if you wanted to cool the brakes a bit
BUT if one of the engines quit, then we would retract the gear for performance.
It is pretty rare these days to leave the gear down to cool the brakes, the only time I can think one would do this is if you were in the traffic pattern doing multiple take offs and landings as in a training situation