You are right about attack speed runes, they are definitely lacking, I never thought about them because I always thought bork+PD/shiv was enough atk speed to reach the cap.

However you are very wrong about the build being outdated, it is still perfectly meta, it's the build that Yassuo, ArKaDaTa, and Hades Underworld frequently use, and they're challenger lol. You are especially wrong about Bloodthirster. Bloodthirster is WAY stronger than Death's Dance on Yasuo.

I'll break it down for you to help you:

When you build Bloodthirster, you get 20% lifesteal on every auto attack AND on every Q, because it counts as an auto attack:

An average auto attack when full build will do 840. The healing from it= 170 HP

An average Q when full build will do 955. The healing from it= 190 HP

You also get a 350 HP shield, which is not neglectable.

When you build Death's Dance, you get 15% healing from all physical damage you deal,which means your auto attacks, your Q, and your ultimate. Your E does NOT heal you as it is magical damage.

Your ultimate is also neglectable for two reasons: First of all, it is more often then not (atleast in teamfights) a multi-target effect, therefore you only get a lousy 5% healing from it's damage, and you only use it once in a teamfight, where as you use your auto attacks and Q's a LOT.

But for the sake of maths let's do it, assuming you land the perfect 5 man ulti, you will deal, with 350 AD, 925 damage on 5 people, so 4625 damage. You will heal for 5% of this damage, which is 230 HP, ONCE in a fight. That's the amount of healing you get with a SINGLE Q when you have Bloodthirster. (minus 40)

Now for the Q and Autos;

An average auto attack when full build will do 840. The healing from it= 125 HP

An average Q when full build will do 955. The healing, when hitting ONE person, will= 145

That means every single auto AND every single Q you miss out on 45 HP if you had BT instead. That literally means that after autoing TWICE you already made up for not healing from your ultimate, and from there on you will keep on outhealing Death's Dance. Think about a teamfight where you auto 10 times and Q 10 times, that's you missing out on 900 HP! Plus missing out on the 350 HP shield, so 1250 HP! Definitely makes the difference between living or dying.

Also these maths dont take armor into account. Which makes BT even stronger, the more armor the ennemy has, the less damage you do to them and the less lifesteal you get from the autos and Q's. That means every point of armor brings your healing from Death's Dance closer to 0 compared to the healing from BT, you have +45hp of margin, therefore BT will always be relevent whereas Death's Dance might get negligible against armor.

But Death's Dance doesn't stop sucking there. Death's Dance actually punishes you for landing your Q on multiple opponents, for the same reason as your ultimate. At the instant you hit more than one person, you instantly cut the healing down to 5%, whereas Lifesteal will still apply the whole 20%.

Let's compare the Q's:

If you hit a Q on all 5 members with BT, you deal 4775 DMG and heal for 955 HP!
If you hit a Q on all 5 members with DD, you deal 4775 DMG and heal for... 240 HP.

That's an insane difference.

The other stats and effects on Death's Dance aren't even good on Yasuo. The +10% CD is useless because your Q scales down with ATK speed and your E already has no CD. Your rank 3 ultimate also already has something like 38 seconds of cooldown.

As for the Bleed effect, the shield effect from Bloodthirster is just better. The shield actively NEGATES damage, whereas the bleed effect only transforms the damage into a DoT. You're still gonna take it in the face.

I made a very lenghty demonstration to help you understand the logic behind Death's Dance suckiness on AoE champions. Very overrated item.

Good luck summoner!

Thank you for the hint about champion matchups, i'll definitely try to update it and explain them more thoroughly.

I also did not explain the mechanics of Yasuo because I assume people reading guides about him will actually invest time in learning them, like EQ-flash-R, they aren't really complicated. Yasuo is more about decision making then actual mechanics. And good spacing/ fast fingers around minion waves. The only mechanically intensive stuff is using windwall and EQR to animation cancel different combos, which you don't even need to play Yasuo at a high level, it's just fancy stuff.