Exactly: you can absolutely always define a market here a company has a close-to-100% market share.
That's why, to actually talk about a monopoly, you need to very precisely define the market.
Take Facebook: Facebook has a monopoly in online, blue-themed social networks owned by Harvard dropouts.
It doesn't have a monopoly on social networks, on communication, on online networks, on online ads, on online ads in social networks, on blue-themed online social networks, and even on blue-themed online social networks with a timeline feature.
