No one will have to worry about who's running where if there is only one class. Sounds like an advantage to me!
It may be an issue for some to pay $60-$75 and wind up with a 5-min main. With one class and 20 min mains, everybody wins.
In the end, it's usually one of these two concerns: runtime or chance to win a trophy or prize. The one class 20 min main addresses run time, but I don't have a good solution for the other.