I believe the problem here is that balancing for both the casual player and competitive player is nearly, or completely impossible.
Look at it like this:
If Deathstroke is nerfed to a near-perfect balance, and requires smart thinking to beat (when he is used by a smart player who knows his tools), yet casuals still have almost the same amount of trouble against him because Deathstroke's options just dominate those who do not put their efforts into the game, there's an issue with continuing to cater to the casual player. If he is nerfed again to the point where casuals can now beat him, what will become of Deathstroke in competitive play?
It's quite difficult to tell when you cater too far to one side over the other. Catering to both the competitive player and the casual player is really rough.