While I would agree that the response times from questions sent to Amazon's support team can be a bit on the long side, I'm not sure I'd characterize their Cloud Drive service as a whole as broken. I've been developing against it for months now. Yes, I've seen some of the issues that you've reported in these forums, but those were eventually addressed. Every app's mileage will vary, of course. I can definitely say that we run our app on >300 mb/s connections with no issues, even when we were still at developer rate limits. Yes, you have to have restraint on the number of concurrent threads you make from a single endpoint. It is what it is. If your app cannot work that way, then Cloud Drive probably isn't for you.
I have no skin in this game. I just wanted to clear up some misconceptions for your users.