That isn’t very helpful considering rocket launches only spend a few seconds in atmosphere mostly going vertically to get above the majority as quickly as possible .

You've just got the problem of building a fixed wing aircraft which can carry your rocket full of explosive propellant, successfully release it pointing in the right direction and then get the hell out of the way....

You're extremely limited by the amount of mass you can even launch from a mothership aircraft.

There's no future in this idea outside of small sat, and probably not even there.