Yasuo should win pre-6.
Post-6 I believe Zed if both people are equally skilled. At this point Yasuo cannot knock Zed up due to Q being dodgeable by ult, unless Zed is bad and gets caught where Yasuo can EQ him. Lategame Zed is trickier to kill and, albeit with the highest skill cap in the game, can ensure a 4v5 with his assassination.
However, there are two variables which easily skews this data. A) Does anyone else on Yasuo's team have a knockup? If yes, Yasuo gets a better matchup lategame. B) Is Yasuo against a team where his Wind Wall can easily change the outcome of a fight? If so, then Yasuo gets a better matchup. Interestingly, Yasuo gets stronger or weaker very VERY directly based on who is fighting, and who he is fighting with.
Tl;dr- IN LANE ONLY, pre-6 Yasuo, post-6 Zed.
1) Totally agree with him that there are people who defend their actions instead of owning up to their mistakes and they are probably the worst people you will ever meet in ranked. You know what I do when I'm doing bad? "Sorry team, I'm not playing too well. Didn't mean to ruin this for you guys..." Not, "OMFG IM SO GUD IF I WAS ON MAH MAIN HES JUST PLAYING FKIN YI WHOS OP!!!11!" Those people get under my skin like no other. And that was only a slight exaggeration.
2) Sometimes though, people might just have a bad game. You are playing as Maokai vs. Warwick and they have an Elise jungle who decides to camp your lane. You end up going 0/2 and you are 30 CS behind. Your mid, who has had no jungle pressure applied from their team and is getting ganks from your jungler who is 2/0 and 30 Cs up himself might then decide to flame you. Now hold on a moment Hashinshin, maybe I'm not doing so hot not because I suck or I am trying to troll, but holy shit the other team decided to make my life VERY difficult. So sometimes, SOMETIMES, there are extenuating factors that you really don't have control over making your life difficult.
3) Flaming someone so bad they don't want to play ranked any more certainly isn't a good idea. It seems like it works, but all they really do is associate you with someone who has asshole-itis. So now the team can bond over you being an ass and get you banned instead of realizing that the person clearly trolling top is the one in need of a ban.
Summary: Great observation, poor handling of the situation on Hashinshin's part.