Smoke too much
Your observations are correct. With the Harrier II wing (GR7, AV-8B etc) the flaps are so large they could not be put down beyond about 30 deg when the nozzles are aft (as in the STO ground roll) without being blown off. So their selection is armed by the pilot during TO checks after which they travel automatically with the nozzles.
As for a down ramp at the start of the deck roll, I agree that would have to help performance. I think its downside (sorry) is the further reduction in space usable by marching bands. You could also use a large hamster wheel as well, then after N revs to build up speed FLYCO (or any of the old guys who used to fire the catapults) could open a flap and let you loose.
Tinstaafl
Too right. 45 deg IS the optimum angle if you are only considering performance (those early brown jobs knew a thing or two). But we stopped our trials at 20 deg because the law of diminishing returns was rearing its ugly head plus a whole host of adverse ship related issues were appearing on the scene. 15 deg is the practical man’s choice as it provides real benefits to the Harrier with negligible disadvantages to the ship.
The ski-jump has been described as the 'runway in the sky' as it just gives you time to accelerate to flying speed. The Russians use it for flying Su-27 and MiG-29s from ships rather than bother with catapults. But not all aircraft can benefit from a sk-jump. You need a high thrust weight ratio to make the most of the time provided and you need to have aerodynamics that provide adequate control of attitude at well below normal flying speed.
Like the Russians above.