[rtempaccount1]

That theory implies a significant barrier to entry for new competitors.

In some markets that is justified. Those where significant infrastructure is needed to compete. For example Amazon's network of warehouses and datacentres would be hard for a competitor to replicate at scale.

For other markets, that's not justified. For example Uber, a small scale competitor can operate with some taxi's and an app. They won't have all of Uber's capabilities for sure, but they can compete in a locality.