I think that this doesn't have to be true at all. Because of slow but inevitable commodification of the core technological concepts that make up their edge toward the rest of the market.

Open source search engines are still years behind what Google can do, but those technologies are much nimbler and easier to customize. Reactive paradigms, dockerization, open source tools for machine learning. Such tools might benefit the small players to allow building technology that might disrupt the big players.

Then again, many of those tools come from the big players which kind of defeats my point here...