Yasuo buys Dorans blade and dagger
There are now no marksmen in the game that can win against him in a pure basic attack duel, or even drop him to 60% health before he kills them. Just by right clicking. Regardless of runes. Yasuo's base health and armor is so high no marksmen can even drop him to 60% in a pure right click duel.
And Yasuo is one of the, by base stats, weakest melee champions in League of Legends.
This is what is wrong with marksmen in a game that typically ends after around 14 and 16 minutes.