Taxiing around LAS in an A320 is pretty hard on the brake temps Especially if the aircraft was coming of a quick turn. It's not uncommon at all to get the BRAKES HOT ECAM after leaving the gate and having to delay takeoff.
So the airplane could easily have had pretty hot brakes before take off and then suffered the G and Y failure. With only ACCUMULATOR pressure available for manual braking of an overweight aircraft, I'd want to be pretty certain those brakes were up to the job. If he didn't leave the gear down after liftoff, The Ground Brake Cooling Table indicates 3 hrs is not an unreasonable cooling period.