Yeah but that's my point, most of the other assassins are inherently safer and have a way of bailing out or protecting themselves.
Talon: instant jump, stealth.
Zed: Shadow swaps and a dive ult that has a built in BAIL OUT button. Way safer.
Leblanc: She has TWO teleports with bail out buttons and can juke for days. Also ranged. Also goes invisible automatically when she's about to die.
Katarina: Instant teleport. Dumps her entire kit in under a second. Resets when she kills someone.
Diana: Ok you got me there, Diana sucks as an assassin. She suffers from the same problem Yasuo suffers from with a lack of escape and having to dive face first into fights.
Khazix: Invisibility, a huge jump, jump resets on kills to bail out, a self healing mechanic.
Master Yi: Immunity to slows. Complete invincibility on his dash, a heal / damage reduction mechanic.
Tryndamere: Self heal, a non contingent mobility move, IMMUNITY TO DEATH
Yasuo: A weak one second shield and a dash that can only be used on enemy players.
When you look at it, Yasuo is by far the least safe assassin other than Diana, and even then she's naturally more tanky than him on most build paths. Laning, Yasuo has no answer to ganks other than walk away, and his movement speed was nerfed so he can't even do that well. In team fights, his ult puts him smack dab in the middle of the enemy team. Sure he can flank but his dash has less range than other assassins and he has no way of bailing out like many others. He's an all in champion with no way to protect himself other than wind wall, and that does absolutely nothing vs melee, ground target, and laser abilities.