Remember they are American. So "subjective and untested interpretations of European privacy law" is a really weird thing to say over this side of the ocean. If the law says "this" then "this" applies. It doesn't need to be "tested" or have a judge "interpret" it. It's the rule, it's quite clear, it's what is supposed to be done; period, full stop, end of sentence.
"and the proposed fine is entirely out of proportion with even that interpretation" - the maximum possible fine is 4% of annual global turnover, so if Amazon reported sales of $113.1bn and they're only asking for around €750M, they aren't going for the full whack. Again, it's quite clearly stated in the rules (and they use turnover not profits because of the creative accountancy that minimises the tax burden).