Mobility is really hard to balance, but it is really fun to play with.
I think That is the main reason new champions with mobility/mobility type spells have been released because it may pose trouble for balance because usually mobility is either hit or miss, meaning it could be really OP or just un-needed. Having mobility on a champion will make that champion more fun, it's just a fact. But at the same time, it can be infuriating to play against or just funny to look at. Bard is a case of a Funny mobility spell that can be used really well but is really Balanced. LB is a case of frustrating mobility.
Since everyone is having mixed feelings about Ekko I think I should give my opinion on that champion right now too. Every single ability he has, can be dodged with ease, but it takes focus to do so. His ult will only hit you if you didn't pay attention to his clone or you were cc'd for 3+ seconds (thanks morgana!) His E is a short dash with a blink built in, but his blink is definitely short range, Think like an annie W. Ekko's W does have amazing uses but it has a wind up time of around 3 seconds and the effect goes away shortly after it lands if the stun doesn't proc. Overall, I think he's in a good spot because he is an assassin, and he will be able to do a lot of damage to you because of this fact. He's squishy enough to die and it get's easier to do so when you cc him. His ult can be annoying to play around and I know we all know this.
Assassins will burst, and this is a fact. But complaining about that fact on the boards will get you nowhere. Ekko's damage isn't unbelievable nor is it unavoidable.
