There is plenty of competition for AWS, so we would, in terms of economic theory, expect that AWS charges you mildly more than it costs them to provide the serv

There is plenty of competition for AWS, so we would, in terms of economic theory, expect that AWS charges you mildly more than it costs them to provide the service, unless they have any particular economies of scale that people like GCP and Azure (and the other less-known cloud offerings) do not have access to. Which seems unlikely to dominate the costing. AWS may be able to charge a surcharge for being the biggest and best-known cloud offering that most people have expertise with, raising the de facto cost of switching.