Every single one of Mag's abilities are great. Shockwave is like a better Dragon Slave, Empower is basically free Battle Fury, Skewer is a great positioning/repositioning tool, and as I've already said, Reverse Polarity is more or less like a Black Hole without drawbacks.
Unless you need someone that can tear up a jungle, why in the fuck would you pick Enigma instead of Magnus? Hell, he doesn't even push as hard because Shockwave and Empower plow right through creeps. Both heroes have useful and varied toolkits, but as far as I can tell the only Enigma has is he's a top tier jungler while Magnus isn't. Also, he's less likely to get banned because pro teams already know Magnus ruins games.