The catapult is just to increase the effort supplied from the engines, the same effect as adding extra engines to the aircraftNow I was going to use an aircraft carrier as an example Chas. I discounted it because of the steam (yes) catapult which is an additional thrust, necessary because of the short runway, and as such adds another dimension to the conundrum.
Take away the catapult and assume planes can get going without and it’s the perfect analogy.