No, I don't think that's accurate. The F2P games are designed to be engaging and fun. If that happens to be the case for you, then you get your money's worth. A traditional subsim could be called a "time-sink" as easily, after all, you spend hours when you play it grinding our convoy attacks.
Did you enjoy World of Tanks? I had not really paid much attention to it before now. I hear it is very successful.