I think that people want purebreds more are because they want good bloodlines, and they might price better when you sell them, i also think mixed are better because you would get a better chance of lots of good and different skills. It's like what people are doing with thoroughs and quarters, quarter were the origional racing horse, then the thoroughs got good at racing too, so they breed them 50% 50% to get a better racing horse(that's in real life). I hope that helps!