With proper strategies and attention (paying attention to 'negative clues' ie. not x value and not y colour, the 6 cards variant is just so much easier.
Looks like we had a bad run of decks then probably if this is the prevailing view. Small sample size.
Regarding variants (not just this one): At the two player level I'd suggest that the biggest problem is the unavoidable back-to-back discard problem, by which I mean that if we both have the same unmarked chop cards there's nothing to stop us both discarding it. Some variant that allows that to be saved would be a nice thing (as that's just being screwed over by luck rather than poor play; I personally don't enjoy it when it happens but imagine others might just think it's part of the game rather than a flaw(?)). I suppose it could be implemented in a couple of ways, for example a token that can only be used in that circumstance which can be played immediately after a turn in two player or an undo button that again can only be used in this exact situation.
Regarding the currently implemented variant: has anyone extensively experimented to get a feel for the "goldilocks number" of cards in 2 player? Why not 7 for instance? 8? How bad (or otherwise) does it become?