Phil R
"Given that the thing will fly regardless if it's going forward quickly enough"
Unfortunately this is not true, or you would be sort of correct.
Harriers need wingborne flight to take-off when heavy.
If you try to throw a stone as far as you can, do you throw it level, or up at an angle?
Imagine if during the entire time of flight of that stone it could accelerate.
The harrier needs to get to a certain speed to fly using it's wings.
It takes a certain distance to accelerate to that speed.
That speed, and thus distance changes with weight. ie you need a longer acceleration distance if you are heavier.
If you just shot off the end of the deck, your maximum acceleration distance to get to flying speed is like throwing the stone level.
If you fit a ramp, then you have given yourself a lot further to accelerate before things get wet.
Essentially, if you use a ramp you can get airborne without actually having enough speed to fly. You are just hoping to accelerate enough before you fall back to the water.