It's not in fact that Yasuo is getting another skin, it's that it's not interesting.
We just had Jhin get another skin and he's certainly a champ that's gotten his fair share of skins over other champs that have been on the waiting list longer, but LOOK at it!
This is inspired! It's interesting and makes use of his inherent theme well while also giving a different take on him.
Yasuo's skin is just a samurai in neon colors. You could do that with a chroma for his base skin. Making skins for champs that already have lots of skins is fine if there's some creativity to it. The real problem is that it's weak. Especially since he's supposed to be a boss character.