Backwards and Others,
A couple of points that might help clarify matters, I hope. (and I've kept to the 1 hour post limit!)
Phil R - the F-35B cannot vector just using the aft nozzle. Any thrust vectoring is done by using both the aft nozzle and the vane box under the forward lift fan while in its 'powered lift' mode. Using these, plus some clever flight control (UK led, by the way) allows the aircraft to move the thrust vector around without generating big pitching moments. Differential aft and forward thrust is used for pitch control.
Another big difference between flat deck STO and a ramp launch is that the aircraft does not have to be rotated before it gets to the end of the deck. There's quite a bit needs to happen in a short time in a flat deck STO, and the videos that have been released show some quite quick combinations of tailplane and aft nozzle movement. Ramp launches are actually a very low risk way of taking off.
Weight penalties - the C certainly carries dead weight, it's just not as visible as the B's lift fan. The airframe is massively reinforced in almost all areas to handle catapult launch and trap loads, and the landing gear is also much, much heavier. Lots of heavy metal. The larger fins and tailplanes needed to provide low speed control also add weight, and drag. The much larger wing also adds weight, but more lift and better cruise efficiency as well as very useful extra fuel capacity. So, that bit isn't exactly 'dead weight'.
I was told by the Chief Designer that the C's 'scar weight' (the extra weight compared with the baseline A variant) was much more than the B's. Doesn't make it a worse aircraft, it still has more range and larger bays, but the B has a better thrust/weight ratio and will probably be a better air to air platform. C will probably have a better 'first turn', but that larger wing's extra drag will probably hurt it's sustained turn rate compared with the B - but that's a bit of speculation.
Hope this helps, and as ever
Best Regards
Engines