According to
this you can just bind whatever key you want to a /command or a console command. I might be misinterpreting that, though.
Plus, hitting the light key a variable number of times depending on my current tool is my main problem. I can't build muscle memory for that whereas t/dup is easy. The New Duplicator only has two modes, so it's always only one press away if I need to switch modes.
I just don't like the toolgun. It just acts differently from basically anything else with its variable number of keypresses. I just find it vaguely frustrating to use.