... until it's used up the upwards momentum* provided by the ramp...
Upwards momentum provided by the ramp? Explain that some more.
Question: does the aircraft's speed increase as it climbs the ramp?
Ever stood on a bow ramp in Sea State 6?
Fair point though and when I wrote that I suspected someone might pick up on it. Are we agreed though, that neglecting ship motion (at your peril!) the momentum comes from the aircraft's engine(s) but that the ramp ensures that there is a useful upwards component? Flat deck - no upwards momentum at deck-exit. Ramp - upwards momentum with the same aeroplane at deck exit. So in a "big picture" sense if not a mathematically-correct one, the ramp provides the upwards momentum. The upwards momentum is way more relevant then the slight KE to PE trade effect on speed as the aircraft climbs the ramp.
To answer you final question, in my experience it always did, substantially. Of course it wouldn't if the aircraft engine stopped working.
Do you think I've answered the original question now?