That is a theory; not necessarily a decided reality.

Google is an ad company; their product is an audience and an advertising system. There is no reason that advertising should be untouchable except at scale. There are plenty of tiny players who eke out a profitable existence at small scale with ads. It is likely there is a path from there up into a mega-giant if someone really goes to look for it.

If anything, advertising might suffer diseconomies of scale for most products. Small businesses want to advertise locally.