I did some checking today with a high speed digital servo (500 heli tail servo) on the FrSky V8 and the FrSky Two-Way verses an old school FM receiver. Yes, the FM is smoothest in movement, there is no doubt about that. There was a roughness to the movement of both of the FrSky 2.4Ghz systems when compared to FM, but neither one stood out as being more rough or steppy than the other. The roughness is very speed dependent, but can be seen at most stick speeds to some degree on my gear too.
I noticed though, if I loaded down the digital servo as it wold be in flight that the effect was damped. I have all digital servos in my 500 size helicopter, and until this thread started I'd never noticed any issues in flight and I still don't. I suspect there are none for most pilots.
The effect of the problem is a bit like having a dead pixel on a LCD TV, to anyone not familiar with the particular TV they would not even notice it, but the owner of the TV will always be looking for it, as it gets 'into his head' so to speak.
I think the issue will be fixable in firmware, but the cost may well be some latency. I gather that some other 2.4Ghz brands have high latency already, and that may well be caused by some of the extra time needed to smooth out the sync issues between the PPM frame and radio frame.
In the meantime I WONT be selling my FrSKy and buying Spektrum.
A. I can't afford Spektrum.
B. I've seen too many crashes on Spektrum DSM2, and repaired poorly designed circuit board soldering issues.
C. I fly 90% analogue servos in park sized models and there is no issue with them at all.
Fly's airplanes & helis, glow & electric.