Why does Kalista and Yasuo even exist?

Because CertainlyT loves his ridiculously overloaded kits and apparently no one in Riot bothers to point out that fact before his champions are released.

I agree, one thing riot should consider is how fun things are for the enemy laner. I don't think they're that broken, just that they are infuriating to play against. Riot could have made a champ that's fun to play as and against, but they decided to pick the wrong choice on these cancers.

Also riot loves mobility.

Yeah, riot loves mobility. That's why they exist. Even though I absolutely hate both of them. It's really lame when you have abilities that they can make almost useless since you should virtually never be able to hit with them. And yet you have to waste mana to try anyways. While they seem to be able to do all sorts of cool stuff and be able to get away with it no problem.