My point is that without having an "H-gate" arrangement (like a manual car gearstick) on a sidestick or control column - which I'm not advocating, of course - then it's impossible to only make inputs which are only in either roll or pitch. There will always be an amount (hopefully very small) of cross-coupling between inputs in those two dimensions
I don't believe that to be the case. The stick's neutral position, in both axes, is fairly certain... it's rather easily maintained in that 'detent' - if you will - of one axis while being moved within the other.