[JumpCrisscross]

> there's an advantage to simply lifting the vehicle that high, it's already starting with more potential energy than it would at sea level

This implies dropping to presumably start a scramjet? Otherwise, all you're getting is a bit of altitude and softer max Q.

The surprise advantage of air-launched vehicles is you can launch from any airfield. The surprise disadvantage is you need strength two directions; vertically, when it's thrusting, and horizontally, when it's hung underwing.