"Choice" can be thought of as a cover-all. It's not like ten is 100% increase over five or is even better than five in the first place. There are so many different things at play.

Look at search engines. What is that, is that a monopoly? A duopoly? Does labeling it based on quantity of production and market share tell us anything about how that quantity of production and market share is impacted by that label? Not really.

What we want to look at instead is all the related incentives. For example, Bing is a little bitch compared to Google. But Bing isn't a little bitch since Bing is one of the main reasons why Google is so good. After all, if Bing didn't try to compete with Google, it is likely that Google would not have improved so many of its offerings in order to stay numero uno. And what about all the other ones like DuckDuckGo or Yahoo? They're not doing much of anything in the market, right? Wrong. Well, maybe wrong. They're not perfect alternatives to Google, people tend to use them for niche reasons. But if Google upsets people enough or if Google doesn't develop one specific niche enough, then Google loses a proportion of its customer base to those others. And this is very bad for Google, much worse than the "incomes" of any people at Google suggests it is.

So, while the search engine market can be said to only have a certain amount of "choice", it can be thought of as operating fully with choice since the producers and consumers in the market are all operating voluntarily.