The history of the cloud computing market belies your argument, in that the entire market has grown significantly since 2020, with all 3 big cloud providers >3xing their operating income (and 3-5x'ing their revenue) over that period. That isn't what you'd expect from undifferentiated, interchangeable commodities.

The scenario you've described sure sounds like the enterprise ideal, but it probably isn't the reality: in fact, some combination of high switching costs, feature differentiation, and/or price insensitivity means you have 3 highly profitable businesses.