I would agree that the script seems to make too many small worlds. However, the idea of making a minimum number of continents naturally would mean those who want small worlds can't play them. I would suggest, seeing as full worlds seem most popular, having two current public worlds - one being only a full world and the other randomised out of the other options. When either category reaches the requirement for a new world, then a new one of that type is made.
I don't think that the number of players is much of an issue at the moment. Pre-multi worlds it was quite a lot higher, and more players makes the game more interesting - as you can have more interactions with people.
One can't expect to have little competition in the larger airports, indeed it adds more strategy to the game, as the largest airports may not be the best places to base.