Aren't the labor laws discriminating at a scale that is several orders of magnitude smaller than Amazon, though? The implied context in the GP is that they're talking about Amazon's size as opposed to, say, Target or Walmart.

Sure, but I was using labor laws as an example to show that there exists precedent to discriminate based on company size.

Further, GP also claims that “being a monopoly” is the only scenario in which size matters, but monopoly power is not about overall company size — it’s about market dominance. You can be a (relatively) small company and still exert complete dominance in a market, and engage in anti-competitive behavior that will attract regulatory scrutiny.