Yeah, I have done much more builds with Yasuo, and literally ALL of them are much more effective than this, I'll start updating tomorrow or later, depends, since it's 12:30 AM here.

Alot of times I don't even build Randuin's Omen I just build the GA and through in extra damage, depending on their team comp.

I know that, otherwise I wouldn't even bother making this guide, but let's say the spell is targeted/AoE/ Targeted Ranged. Sure there's wind wall, but Compared to pretty much, EVERY non-ulti skillshot, Wind Wall has a significantly higher cooldown.

You know it is possible to move and dodge skills in league of legends, right?

Hmmmm, spent the past few days experimenting with a friend's account (he left and he wanted me to farm him ip for runes), you do seem to have a point, however, the reason why i take Warmog's is,

It gives a pretty good amount of 1k hp, it also provides some hp regen depending on your level, usually from what I've played so far, including the fact that sixth item is up to you, If you take randuin, you're suspectible to magic damage instead,(although Warmogs and Guardian seemed to have worked so far), taking banshee for the spellshield means one of them can just pop it with a not important spell, although considering the update, they only have 25 seconds i think before it appears again, Guardian though, I see no reason to not get it actually, it seem to've worked well if i have warmog's, otherwise the enemies just continue ff'ing me, which is another reason why i got warmogs, that way you can tank the damage a bit, although no armor and mr given, which, can Be treated with per level armor and mr runes

But Warmog's Armor isn't a great choice.
Randuin's Omen > peel, armor, ditching of focus
Guardian Angel > revive, tactical choice for an all-in and son, armor and magic resist
Banshee's Veil > spellshield, avoids initiation on you in the first place

Your free "core items" should be offense in general and if behind maybe your build might consist out of two offense items when being behind.

While I do agree that glass cannon Yasuo is epic, Note that this build is technically 5 items only, 3 are core (Warmogs, Statikk, and Infinity), 2 aren't (Boots and Bloodthirster), actually, including boots, this is more of a 4 item build instead, for a full build, it's gonna be (In order), Statikk, Mercury Threads, Infinity Edge/Warmog's Armor, Last Whisper/Warmog's (if you didn't take Warmogs as 3rd item (Black cleaver is for the sole purpose of helping your teammates deal more damage, otherwise, always take Last Whisper), Guardian Angel and Bloodthirster, asides from the defensive items, It's exactly like Glass Cannon, just with Warmog's,

Glass Cannon Yasuo works fantastic early on and rather more Warmog's Armor isn't the best defense choice. After getting Statikk Shiv + Infinity Edge + Last Whisper you might wanna build a defense item like Guardian Angel, Randuin's Omen or Banshee's Veil.
The best furthermore offense choices are Blade of the Ruined King and Ravenous Hydra ( Bloodthirster).