If your motor is a 3 phase brushless, then there should be no need for a main power switch. Instead put a simple, cheap, reliable key switch on the low power input to the controller's logic section of the controller. Even my 20-30kw builds don't have or need main power switches. Safety features include an appropriate fuse at the battery, a key switch to cut power if all else fails, and ebrake switches to easily and intuitively cut off a runaway condition without letting go of the handlebar with one hand.
Elimination of unnecessary components is always the most elegant solution to me.