...Why not just nerf the movespeed of all Mobile Champs?
Base movespeed is all over the place in this game, but if it was properly organized it could be the simple answer to mobility creep. Champions like Kalista can keep their dashes, but in return should have their base movespeed nerfed to 300 vs. champs like Garen who can keep their 345 movespeed (or even have it buffed if needed). This makes mobile champions way more high risk/high reward - as they are supposed to be. Misplay one dash and you'll pay for it with a +45 movespeed Darius charging you.
**Examples of how retardedly random base movespeed is right now: **
350 Movepeed:

345 Movepeed:

335 Movepeed:

** Examples of how it could/should be:**
350 Movespeed:
345 Movespeed:
310 Movespeed:
300 Movespeed:

who already have lower movement speeds
with moderate speed
should have the lowest
in movement speed with
on top of his high mobility, I think there's a slight issue there.
on the other hand, has 10 less.