Right now most of the evil exit nodes would be people who have evil use for the data. They are willing to put out more money and have more money for making them faster (Evil governments, Org Crime, Ad companies). So right now, getting a faster connection could be a bad thing. This would help even the playing field a little.
Sill, they need to do a lot more. With the tor network you don't need to control any nodes if you have control of a few routers along the way (Governments). Look up: Wei Yu. Replay Attack still make it easy to know who sent information to who. If it is not End-to-End tor, they know what you send too.