Competition doesn't have anything to do with number of players. As long as there is more than one party and they are not colluding, they will compete for each others market and push prices down or increase the quality of service.

Pro-competition laws aren't about what's fair for other people that might want to compete, they are about what's best for consumers.

Yes. Isn't a basketball game a competition?

I remember seeing a paper that in any market where the top 4 players have more than 60% of the market, they'll naturally behave in a cartel-like way in terms of pricing etc.. So it's not ideal. But still, two players seems much better than one in terms of, if nothing else, limiting quite how much customers are soaked for.

It is competition, but whether it's enough competition to achieve the beneficial effects we usually associate with a competitive market is a different question entirely.