The way FC workers are treated is not ok. It's the main blemish on a company I otherwise respect. "Other companies treat FC staff like shit too" is not an excuse.
Disclaimer: Work for Amazon (corp / tech side). Opinion my own, obviously.
How is this not an excuse? Most people would switch to Walmart/Target/Bestbuy or any other retailer if the price on Amazon is higher.
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."
The answer is federal legislation. How break time, overtime after certain # of work hours in a day, parental leave.
If we want people to have a certain quality of life at work, I don't see any purpose directing any energy at certain large employers. All efforts should be direct to politicians, who we can vote in, to provide that quality of life at work.
The US did that and the governments solutions was to pass laws allowing for unions. By unionizing these employees are doing the thing the government has already determined will help them.
Otherwise Amazon is leaving money on the table by not already charging higher prices, which is a bet I would not make.