I think the electrician meant 600 watts. Having said that, there are the actual watts an LED consumes vs effective watts, which is how it compares to an incandescent. You need to know which the 600 is. 600 watts for a garage sounds like a lot so I'd assume that's effective, but don't know. It will say it on the fixture/bulb box. Electrician will know.
If you are using a dimmer, I'd suggest using an on/off instead, not sure ambiance of a dimmer matters in a garage.
If that doesn't solve the heat from the switch, split up how the lights are wired so they are on separate switches, and create a scene between the switches so that they act as one and all the lights go on/off at the same time