Stun is a type of slow

I was just thinking that technically a slow is anything that reduces speed, as such wouldn't a stun be considered a slow, because you're reducing the target's speed to 0. This occurred to me when I was playing against a Master Yi, and I was wondering why a stun would be able to stop him, despite his ultimate reading, "being immune to all slows". Another similar case is a knock up, when you knock up a champion they're halted from their movement for a single or more seconds. As such it would make sense that a knock up is a slow as well, since you're reducing their current speed to 0 (they stop moving). Keep in mind that I am referring to their current speed, and not their potential speed shown under the list of stats of your champion in game. I understand that this may cause many changes to the game if applied, (Master Yi Ult would be broken), however I do think it is a viable point to make. Just wanted to hear Riots thoughts on this.