As fun as it would be to run Mega Lucario, its cost doesn't justify its use. With a 3-energy, 140 damage attack with an effect that shouldn't need to go off in the first place on top of a lack of a Spirit Link, you're not going to get much mileage out of it compared to, say, Primal Groudon, who, despite his higher costs, is at least immune to Lysandres and the like.