Reminds me again of "when you don't have to pay for it, you're the product, not the customer". Here, all the free players are opponents necessary to attract the whales.
But that applies even to paid games. It's very hard to attract players to games if it's mainly multiplayer and there's no one to play against. Both players and developers do want an active playerbase, and free to play significantly lowers the barrier of entry for potential players.
So maybe free-to-play simply has to be the future of multiplayer games?
And yet they put me off because you're constantly confronted with mechanisms designed to make you pay. I don't mind paying for a game, but once I'm playing, I want to focus on the game, not the payment.