Won't be guaranteed to work. I'm going back in time a bit, but there a game called Warhammer 40K (most players here have probably heard about it.) When the company that makes it was founded one of the founders wanted to be on the balance team. he playtested all changes to the armies before the updated codexes were published.
There was a huge problem. The guy sucked. Not a little, a lot. All the rumors/gossip about him was that he needed a huge advantage built into the rules if he was going to be competitive. But he was a founder and he had his favorite armies. Guess which armies were almost always better than all the others.
I understand that he's not as influential as he once was, but the lesson needs to be remembered. Balance testers are not perfect. If you get one who is horrible. (say with making dashes work) then he'll complain that the champ is high skill and the power isn't useful. Then it gets into the hands of someone who practices how to use that skill and we found out that the champ is broken. (Ahri, Kalista, Lee Sin).
But since the balance team members did play the champ (not enough times.) and tested out the new skills (that they may not have the skill to use properly), Riot believes the problems are not balance/kit related. At least that is my impression. They don't test enough, don't test properly, and don't have master level players testing the champ against diamond level players enough. They need to know how oppressive a champ can be if properly used and I don't see that in their comments about balance. Instead its about "this champ is fun to play." Nothing about the champ being miserable to play against.
(Sorry, just got out of a game where a ranked Ahri and 4 smurfs proceeded to smash my team made up of level 14-22 players. It not only wasn't fun, but was a great example of some of the problems Riot should address in matchmaking and in champion balance.)
