If that were solely true, there would be a lot more competition in the field right now. Amazon, (and to a much lesser extent the other 2 big names, GCP and Azure) are so massive not because they have a lot of power (plenty of other companies like digital ocean or OVM have plenty of scaling power too)— but because the integrations between their products are so seamless. Most of that functionality has a foundation in FOSS software that they’ve built on top of.