Uhhhhhh, No, I have had the same problem. As I have moved from an Ego of 2,000 to just over 80,000, the opponents that I have in the Arena very regularly have 30% higher Ego than I. They are never more than 2 to 3% lower (at least this happens very rarely). In other words, it doesn't matter what you get your Ego up to, opponents are chosen based on Ego and 80 to 90% of the time have higher Ego and in the neighborhood of 80% of the time, completely unbeatable. Another thing to look at would be to give the boosts a percentage boost rather than a score boost. When attack is less than 1,000, getting a 200 point boost is significant. When attack is close to 20,000 a 200 point boost is virtually worthless.
While not so much now as it was when I first started, if opponents were chosen based on amount of time since starting the game, I would have better situations.