Working in an Amazon warehouse would not be considered a "trade" by most definitions. It doesn't require much if any training and amost anyone in normal physical condition can do it. It's more of a pure "laborer" job, these have always paid less than skilled trades.
You've missed the point. Very obviously working in an Amazon warehouse isn't a trade. The point isn't that working at an Amazon warehouse is a trade, nor the job's actual wage...
The point is that two jobs with superficially equivalent wages can be far from equivalent in things like the toll it might take on one physically...
The same could be said for the starting salary of graduates with undergraduate accounting degrees and entry level plumbers ($40k-$50k annually)... Similar in terms of wages, far from equivalent in terms of physical demands...
