I thought amazon was also a bubble of some kind, relying on aggressive growth to swallow the market and then change it's policies because it's unsustainable ?
Musk seems a little more down to earth (sic) here.
Amazon didn't turn a profit for years because they were heavily reinvesting in more/better infrastructure (their "fulfillment centers") and services. One of the biggest services out of this reinvestment is AWS, which AMZN built for AMZN, and then realized it was such a good product they started selling it to others (also part of Bezos' ethos and their large initial costs: if you can't sell your internal tools to other people, you shouldn't be using it)
However, Amazon is making a profit these days, and is still growing, so I think it's sustainable.
Uber, meanwhile, is/has been subsidizing many/most rides with VC money in order to get market share, which is an entirely different thing and more in line with your perception.
Musk seems a little more down to earth (sic) here.