Ekko is one of the most balanced assassins i've seen
For all you people complaining about how "op" ekko is, consider this.
An assassins job is to 100-0 the most fed person on the enemy team.
A few examples of this are

Riot has been literally forced to gut almost every assassin due to the fact that they
can 100-0 you with minimal effort. Champions like
can almost never be "balanced" due to the nature of their kits, they can deal too much damage with too little effort involved. They literally just point and click a few abilities, then dash out.
Where
stands out is, yes.. he can 100-0 like other assassins, but that damage isn't so front-loaded and unavoidable that his counter play is almost non-existent.
When a fed
or
jumps on you, what can you honestly do to escape? Nothing at all, they will just use their stupid easy point and click CC / resets to keep you in 1 place and 100-0 you while you just wait to hit the respawn button.
When a fed
jumps on you, what can you do to escape? Tons. You can easily predict where he will throw his W, you can dodge his Q when it comes back around, and his biggest damage spell literally TELLS YOU where its doing to do its damage. All you need to do is keep ekko moving and dont be stupid enough to walk into this ult and you will have at least SOME chance of escaping or even winning a duel against him, even when he is fed.
And yes he is mobile, but ekkos ult is a double edged sword. He can use it as an AP nuke to do a shit ton of damage, but afterwards he is pretty vulnerable so its usually best to NOT just blow your ult that way. Ekko can use his ult to escape or commit, not both. Meanwhile

and others can just play Mario Kart Double Dash and race past you if something goes wrong.
So for all you people complaing about how ekko is too mobile with too much damage, id rather have 100 assassins like ekko roaming around that need to at least put effort into killing you, than a bunch of fizz, zed, katarinas, ect who just jump in, point and click, jump out.
And this bad ass of an assassin can get triple kills in team fights within 3 sec flat. W+E+Q+Hydra Aoe out the ass and massive damage output. His waveclear is instant, he can clear a creep wave in a few AA's, clear a jungle camp in -1 sec. hes a beast
is either OP or broken. They are low risk/high reward and they snowball WAY too hard.