Climbing to altitude is the straightforward part. The transition from zero knots to the stall speed of the aircraft (minimum speed at which it can remain airborne) is the tricky bit. Designing for a lower stall speed necessitates wings which produce higher drag (by being larger) which requires more propulsion, which means bigger batteries and motors. So launching from a catapult or rocket or mothership or whatever means a lighter plane.
Launching by rocket means the plane would have to be pretty rugged to survive it. And that means more weight. You also have the issue of deployment. Folding wings means more weight and more things to go wrong.