Percentage Steroids

The way that speed-ups and slows interact in League leaves speed-ups feeling very unrewarding. Speed-ups manipulate BASE movespeed, while slows manipulate CURRENT movespeed. To give an example, if two opposing Zileans use their E on a target (applying a 99% speed boost and a 99% slow), the two combine to form... a 98% slow. The mediocre slow from Rylai's or Frost Queen's can more or less cancel any speed boost in the game.

On top of that, it's just unintuitive; percentage steroids of the same kind combine additively, percentage debuffs subsume each other and combine multiplicatively with steroids. I think it would make a lot more sense from all of these perspectives if percentage modifiers (crit chance damage, movespeed, attack speed) all combined additively. A few balance or tooltip tweaks could remove any impact on some of the stats completely ("Yasuo's critical strikes deal 180% damage"), and it opens up a lot more opportunity for speed-up skills; isn't it telling that Stormraider's Surge, the most recent speed-up skill released (not counting Jhin's weird crit-ghost mechanic) gives slow immunity?