That claim is very specific to how you define market. Most markets have never had more than 3-5 major competitors in them because beyond that it gets too hard

That claim is very specific to how you define market. Most markets have never had more than 3-5 major competitors in them because beyond that it gets too hard for customers to differentiate between them, too hard to understand all the available brands etc. But this depends on a lot on where you draw the boundaries of the market. There probably aren't more than 5 good Chinese restaurants within walking distance of where you live even in a city, for example. But over the whole city there are many more. There are only ~4 main cloud providers globally, but if you expand your definition of the market a bit further there are many more. In practice for price competition to exist you don't seem to need more than 3-5 players. For example Oracle offer a generous free tier in the cloud space.