I wouldn't call it an issue, but rather a feature. Smooth mode is called "smooth" for a reason. Electric motors produce their maximum torque at 0 rpm, and the Air produces truly prodigious torque. Smooth mode deliberately retards initial throttle response so as to make it easier to launch the car gently when keeping passengers calm and collected is the priority.
If you're wanting more punch off the line, Swift mode picks up the pace more quickly. Sprint mode, which unleashes an instant tsunami of torque, can make your passengers want to vomit . . . if that's the mood they've put you in.