@Riot Design Team RE: Fiora rework and mobility mechanics

So I've been seeing a trend with mobility mechanics in champions of late - "Hit the enemy, then get a speed boost so you can retreat with relative safety."

Gnar (one of my current mains) - Hyper passive Ekko - Champion passive Fiora - her weakness passive

I've also heard about the desire to balance risk/reward with champions in order to allow for better counterplay. Doesn't this mechanic seem anti-risk/reward oriented by reducing the risk of being punished for all-in engagements/skirmishes?

Conversely, the speed boost can be used not just to run away from unfavorable trades, but can also be used for sticking to the target.

By no means am I saying this is a "bad" mechanic. I am just trying to understand in a game where the meta is consistently about mobility where the mobility creep is coming in to play with regards to champion balance and interaction, particularly when you have items like Phage that can do this already, or make a champion who already has this type of mechanic even more explosive?