Apparently working at Amazon is damaging to your career.
Realistically I'd argue it's more on the high end of the "B" tier, but that's neither here nor there.
Amazon's attrition rate is insane. Not high, insane. This should tell you a lot about what it's like to work there. I too learned a lot, and it continues to pay dividends on my resume, so I guess that's how they get away with it.