1-party = voters have no choice, therefore that one party can do whatever they want. 2-party = there is some choice. There's an "in power" party and one opposition. The opposition acts as a limit of what the "in power" party can do, because if people are unhappy, they'll vote for the opposition.

Sure, you can't choose what kind of opposition they want, which most of the times leads to a "least bad" voting. But you still have a way to influence government.

Having some choice >>>> having no choice.

I never 2-party is enough democracy, but it is still way more than 1-party. It's not just a 2x increase. "Democracy" doesn't scale linearly with the amount of parties.