The seemingly oxymoronic concept of monopolistic competition actually exists. If Harry Potter books became too expensive, people would switch to reading Artemis Fowl. If the Goko implementation left something to be desired, people would switch to Isotropic Innovation. Even pharmaceuticals protected by patent law can be substituted by possibly less efficacious substances.
For leisure activities, I think this concept applies too well to be interesting/noteworthy. They're all pretty trivially substitutable, since one can do basically anything else with their free time. It doesn't have to even be a game to be in direct competition.
The fundamental question is always "how much is it worth to the customers"? It has to be pretty good to compete with everything else I could be doing. Dominion is that good. Isotropic was that good. Goko is not that good.
If Goko fails, I hope the lesson learned is about poor execution and not product viability. The freaking game sells itself as long as you
just don't screw it up. FWIW, I also think that would quickly become clear with a little true competition.