Hear me out... if you don't remember, they nerfed the duration his shield lasts (twice, first time from 2 seconds to 1.5 and second time from 1.5 to 1 second), it almost dissipates instantly as soon as you take damage. So the boost from 60 to 100 does NOTHING except block one basic attack (like it did before with a 60 damage shield), but now his lane phase is even weaker due to the fact you need to run in circles for even longer to charge up the shield (and overall mitigate less damage than you would before with the faster charging 60 damage shield). This would be a solid buff if the shield lasted 1.5-2s, and considering his W doesn't generate passive flow any more, why would this be such an issue? It was only a problem before because you could proc the 2s shield multiple times in a single fight by dashing everywhere with his E.
The ONLY way this is a buff is if you have a lane opponent that doesn't bother hitting you with a basic attack before actually trying to hurt you, and if someone is doing that then they are simply playing the match-up wrong and it can't be used as justification for a "buff".
I'm not sure if this was intentional, but considering how Yasuo has been over-nerfed into the ground non-stop and now Riot finally claim to give him some love, I'm not convinced.
EDIT: I was directed to this thread: http://www.reddit.com/r/leagueoflegends/comments/3477cn/the_58_yasuo_changes_arent_a_buff_theyre_actually/
I must agree with the OP, even with Phreak's compelling argument from a mathematical perspective, it doesn't change the fact that his laning phase is still weaker. The shield doesn't matter at 0% or 99%, it can only be utilised at 100%, and even so at 100%, the shield doesn't do enough to justify how long it takes to charge up.