Why can't Yasuo's 'w' block tower shots, but assassins can?

Ok I admit Akali isn't really 'blocking' tower hits, but she becomes COMPLETELY untargetable when her shroud is up so she might as well be blocking them. And Fizz can just press 'e' and dodge them completely (and like Akali become COMPLETELY untouchable). Now back to Yasuo. When Yasuo was still in development there was a time when his wind wall was able to block tower shots, but Riot removed this because they thought it was too strong. Fast forward to today and we have sht like Fizz and Akali making turrets useless. If making turrets useless was too strong on Yasuo, why is it acceptable for assassins? With Yasuo's windwall he doesn't become completely untargetable, and if he wants to tower dive you he has to leave the safety of his wall. My point is Yasuo's windwall may be annoying but it doesn't offer the safety that assassin abilities offer and he isn't able to dive with it. There's a reason why Akali is being picked in LCS and not Yasuo. It's SOOOOO fcking easy for her to start drawing tower agro with her shroud (meanwhile taking no damage at all) and then her team just has their way with you.