The stock has some weird mechanics about how the rocket trajectories moves. At a certain distance, the rocket travels so it reaches that spot, then goes left and passed the crosshairs. However, if you point at an object close to you, the rocket just travels straight, always to the right of the crosshairs. I don’t have a video link so sorry.
But anyways, this slight change or unreliability may not seem like much, but hitting airshots usually means the enemy is strafing, so you want your rocket aim to be the most consistent as possible. The original shoots straight, but stock does some janky shit.
Other than that, there’s no big advantage or disadvantage to using stock or original. Each has their benefits.