Well he is right about one thing. W3W is useless for navigating as there is no logic to the grid it uses, but it wasn't really meant for that. With the Nat Grid you can easily divine if your required location is N S E or W of your current location.
As for his point about blizzards though - if you are out in a real whiteout, a map and compass are also virtually useless for working out where you are. Even if you start from a known point, errors soon creep in if you can only see a few feet so you would have to be a lot more practised than the average punter Under those circumstances, I prefer my electronic aids that can tell where I am to within a few feet. Using electronics in really bad visibility, I have almost literally bumped into my target before I have seen it.
I still have W3W on my phone though. That way, if I need help, I can give my location in W3W, National Grid or Lat Long, whatever the person on the other end wants - under those circumstances, it would be no time to be proud