How much email flows through gmail? Should Amazon have 50% of all ecommerce transaction data? How much of the chat space and social media does Facebook own?

You're not wrong, but I think rather than bringing up counter-examples, you've produced a list of similar problems.

When someone tries to find a new website someone told them about for the first time... what % of that is filtered through Google? If it's a majority, which I suspect it is, then it's still definitely a problem.