I'm not sure with the math, but it looks like it's setup to last hit under turret safely, then rest thrown into as. You could look up the cost effectiveness of runes to be sure.
Let's see here:
1 Attack Speed Quint = 717 IP atm, so 2 = 1434 for 9% attack speed.
So that build would:
Make you lose 4.5 attack damage from the quints
Make you gain 9% attack speed from the quints
Giving you 10.45 AD, 9% attack speed.
VS
6 AS red marks, giving you 10.2% attack speed at 1722 IP
You'd lose out on the attack damage from those 6 red marks, so youd have 9.25 AD
So in actuality:
The "Piglet" build gives you 10.2% AS with 9.25 AD vs. what's been suggested her which is 10.45 AD with 9% attack speed. So the difference is, what matters to you? 1.2% more AS or 1.2 more AD? In terms of cost effectiveness, obviously AS always wins because of what you've previously mentioned. In application? I'd be dumbfounded if my CS came down to 1.2 more AD; however, late game 1.2% more AS could be a little more beneficial because percentages scale better.
But it's like... so fucking close that it's so irrelevant to a guy like me to compare the two builds.
The point is: y'all suggest AS in your ADC builds. Why? Why would you go full AS runes as a korean? Wouldn't last hitting be...really hard?
K, here's the theory behind it. Since attack speed is the most costly stat to get through items (zeal and zerks and what have you), it makes the most sense to get the most of it that you can as a base, as attack speed items tend to give little to no other bonuses except crit and move. I believe the average gold value for every 1% of attack speed is somewhere around 100 - 200 gold. So by getting 10% attack speed, that's at around 1000 ish gold worth of stats. And if you never get pushed to turret, or have a really good support, you should in theory miss very little cs. In fact, you can actually improve your cs if two minions get low at the same time, you can more often clear both without using mana. And as scales better into late game, procs more dorans blade in the early game, and is more beneficial on average to clearing camps than flat ad.
In theory.
In practice, the circumstances make it very difficult to pull off flawlessly, and it makes you scary weak in the early game, so supports often capitalize on this by early aggression.
Last htting with lower ad also can cause you to get pushed in, as you have the enemy minions living slightly longer because of having to wait longer to hit them.
However, if you can get past all that, it has the best scaling out of all possible rune setups. Plus if you're really, really good at last hitting, the lack of early ad is negligible.
I'd say go with what makes you comfortable. I like running armor pen and attack speed with only around +5 or so ad because I play pretty aggressively, so the early pen lets me trade better and creates an invisible layer to my actual damage by hiding some of it in pen. The flat ad is there to capitalize on it, but I find doran's blade gives the amount I need for ad to stay strong. I'll usually have around high 60s ad with high .6 to .7 as and 5 flat pen for most adcs at level 1. I've found that to be my comfort zone with adc starting stats.
So really, it's whatever works. I'm experimenting with pages that run more pen and put some of the as on my blues with scaling mr on the remainder to hide more of my damage at the slight expense of some defense from spell harass from supports. And hybrid pen on mf. Or pure armor pen on urgot. And I usually mix 1% crit mark in for a possible instant win with trades.
So ya, whatever works. Just understand why it works.
I Broke THAT Plateau