You're making a lot of assumptions, the biggest being that the amount of gladiators allowed into the blood games will remain fixed and I'm pretty sure Nate has said as time goes by he'll open it up to more and more gladiators. The second assumption is everyone thinks like you do. I don't think there is only one competition, I find the arena to be very competitive and enjoyable, I also find the arena challenges to be competitive in regards to seeing where other gladiators of similar level are. You are also assuming that the game is never going to expand with new content, new competitions, etc.