Threading cables can be fiddly on anything (though there's a special place in hell for SRAM twist shifters). As you say, it may be tricky in non-optimal conditions. But I don't think anything cable-based is going to be immune to that, especially if you haven't had much practice to develop any special knack that may be involved.
The main roadside fettlability advantage of these simpler types of shifter is that if the cable breaks or severely frays at the nipple end, it's reasonably straightforward to get it out. There's a secondary advantage in having the bend in the cable exposed so that (particularly with bar-ends) you may see or be poked in the finger by the first broken strand as a warning that it's starting to fray - greatly improving your chances of not having to sort it out at 2am in the rain.
Can't speak for brake levers - all my bikes with cable brakes use MTB-style levers, where again extracting a nipple with a frayed stub of cable requires little more than a bit of poking with a pokey thing, and everything's easy to get at.
Murphy's law applies, regardless.