I think the pertinent question should be: how much of rent seeking can Google engage in. That is the real underlying problem. A company does not need to be a monopoly to engage in rent-seeking. All it needs is position itself around a resource and act as a gatekeeper, platform holder, go-to person etc.
Thus, even though Google is not nominally a monopoly, it can still extract disproportionate profits compared to the value they add to the economy by taking advantage of its position in the advertising, search and mobile markets.