My Opinion: Leon needs a buff. He was released too strong, I will admit, but recent new brawlers released have been strong as well. *cough*Sandy*cough*. Leon's super makes him go invisible for 6 seconds now, while Sandy's lasts for 9 seconds and hides 3 brawlers. With no star power, Leon can't actually go much farther than Sandy's super radius. His attack is good but not op and health is fairly low considering his attack damage. Invisibility being unique is what made Leon good as a Legendary assassin. Now, that is taken away. Sandy is better at invisibility, in addition to the fact that Sandy's Rude Sands star power counters Leon's invisibility pretty hard. Sure, with practice he can be very useful but IMO he isn't very Legendary anymore.
(Btw I do have Leon, I'm not just ranting here. These observations are based off of what happens in my gameplay.)