I am not a labor economist, but am a PhD working in the private sector.
My personal belief: in an optimal world people would get a UBI, say 10-15k/year, and would not be forced to work 40 hours a week to get health benefits. I think this would be a win win - industry would replace more workers with capital and those remaining would be more productive and spend less time fixing the messes of those that create more work instead of doing it. If we had this, managers would be less inclined to keep someone out of pity as well - for despite all the talk of harshness of bosses, what I have seen more in white collar is "idiot keeps job because is reasonably liked and has family to take of."
So I say that because I do not think Amazon is the reason for all those problems. To me, the concern I have over concentration of market power is if that market power turns around and buys political power. In a pure sense, I can envision it being socially optimal to have one mega corporation operating a nationwide autonomous drone logistics network (which is what Bezos sees as the future - and it is obvious that is going to happen). I could even envision the political power being important to getting to that goal because there are a lot of laws that need to be written if we are going to have an autonomous drone logistics network - the hurdles are not technical at this point they are legal and societal acceptance.
But where I could be concerned is when the power gets out of hand and they start pulling the levers for whatever reason they want. What if Amazon becomes the only practical delivery agent for all consumer goods. They could be like railroads on steroids if they get into autonomous drones that can ferry passengers as well. Before we know it, they could be dictating things that we as consumers may not put up with if we didn't have the huge switching costs that comes with having a sole provider.
I don't know what those "things" are. But look at Facebook. Innocent picture sharing site right? Well they were slow to react their product being used to help massacre civilians in Burma (or whatever it is called now). Amazon is fairly innocent I think so far.
I do fault them for having crappy labor standards at their warehouses but I think its because they view humans as a unfortunate crutch they have to rely on until they can figure out full automation (much like Uber, which is why they don't really care about treating their drivers like carp (the fish is uncensored apparently)- they think its a transitory placeholder while they gather data). I do wish labor standards were such that you couldn't fire someone for small reasons and then re hire them back as a form of punishment.
But as far as the pay and hours, well I go back to the beginning. I think society should set a bare minimum subsistence, such that you could live in a 1 BR apt with a roommate and work menial jobs, and still be able to get by. I'm not talking about free cell phones and internet. I'm talking raman noodles, a mattress, and a roof. If you had that, employers would need to offer more to menial workers to entice them to get out. In turn, they could be more selective and also more incentivized to switch to more robots. As it is now, Amazon's primary whip is the fear of destitution, which is the market power that all purchasers of labor have over us.
As an aside, take it from someone that has worked white collar/Finance for 5+ years. I am in favor of a 50% tax on corporations. Heck, 75%. No reason other than this. It would finally force them to take a hard look at all the made up/BS jobs they have given their buddies as rewards for showing up for a few years. Maybe shareholders would suddenly realize the company has about 2-3x as many line managers as they need. At places I've been, the ratio of managers to workers ("individual contributors" as they call it) makes the dreaded "administrator to faculty" ratio look benign. They all put manager at titles of people that they like, give them 1-2 people that could very well do their jobs unsupervised, and they all go sit in meetings with others in suits all day.
I am joking of course about the tax. But its not wrong, the wastage.