It's not just about wages. I think Amazon has actually made great strides by raising their minimum wages to $15/h. According to US stats the monetary benefit from unionising is about +11% on average. By offering twice the federal minimum, it's possible that Amazon is already above that. Now, you can argue that minimum wage should be higher still, but that's a separate discussion.

I don't think we should pretend that FC jobs will ever be super high paying or enviable jobs, but there are other ways to improve worker conditions. e.g. In some FC's, people allegedly have to walk for 20 minutes to reach a toilet. That's easily fixed. Making sure people don't have to choose between feeding their families and casting a vote in the election is another example. In general, even for a low skill job, pressure shouldn't be so high as to burn people out.

I think some FCs might actually have decent worker conditions. Others don't. As you alluded to, a company has financial interests that may not align with worker interests, which is why I think this needs to be approached in a structural way. Like Bezos himself once said: "Good intentions don't work; you need good mechanisms to make anything happen."