Amazon's argument, when I was working there from ~2011-2013, was that they had few perks, hard work, but that they paid better than other companies giving employees more freedom to choose what to do with the fruits of their labors.

I don't care for that argument generally (as I personally value my free time well beyond what anyone is willing to compensate me for it -- call it personal utility if you like), but even so, the argument only works if it's actually true. In my experience it is not; Amazon's compensation lags other "Big 5" companies considerably, but some of that lag is hidden in things like their 401k match policy and the delayed stock vesting.

True, but Amazon supposedly rewards their employees well to compensate for the high productivity expectations. The Amazon 401k isn't terrible, but it definitely isn't great. (It's ranked the lowest in the top 50 on the S&P.)