Those two aren't mutually exclusive
This, currently on the front page...sure doesn't sound like Excel is a monopoly https://foundationinc.co/lab/the-saas-opportunity-of-unbundl...
FB has a monopolistic-power in the network effects like you said, but even then entrants like Snapchat show that the network effects can be gained for new competitors.
Now Google may not have done any of the above with search, but it's likely possible to argue that they have unfairly promoted their own products over others, or "unfairly" chose to not list certain websites.