The opponents should increase in difficulty, each time Daisy levels up and a little bit when you upgrade your car.
Currently the outcomes for races are determined by taking the score for your car and multiplying that times the amount of clicks you do. Then the opponent takes into account your car's score and Daisy's level and some preset constants to calculate the opponents score. If your score is higher than your opponents, then you win.
I was worried about trying to balance making the race too easy vs too hard, but looks like I missed the mark on that one.
My larger vision is to make the race game into a top down racing game that you can use WASD for.
As for the models of the opponents being random, I would like to end up making a tier system of the opponents and having boss battles, so that it should make more sense. I've also seen someone suggest a rival character and that is something I would like to explore at some point.