No, it's not rigged.
It's all a matter of strategy.
1. Rush is best up against a steady horse.
2. Rush is best on a short track.
3. Tank is best on a long track. Especially against a fast-starting horse. (Like Rush and Swift)
4. Swift can beat almost any horse on a short track.
5. I think Rapid is the hardest horse to beat, even on the long track.
So it's all a matter of what horse does best on what and against what. You'll find that you can win money after all.
Good game, I like it!