This build only gives you 90% crit, I didn't say anything about crit damage, and you easily get enough base damage for the crits to hurt. This build gives you the best stats for consistent DPS, you can test it vs other combinations but mathematically, if you are on a sustained damage ADC, this build will come out ahead every time. You obviously want to rush one of the BF sword items first, usually IE, then one PD, LW then either another PD or the remaining BF item, depending on the game, working boots in where appropriate. In fact, speaking of boots, you also get more DPS late game selling them for
, if you are on a champion where it makes sense.
Edit: I ran some numbers using teryds league simulator, which hasn't been updated since patch 4.18, so these numbers are a not exact
gets 744.3 DPS
gets 885.3 DPS
since patch 4.18 5% crit chance has been removed from IE and added to phantom dancer, meaning that the damage difference is now much greater than these tests showed. Also, swapping Triforce for an second PD granted 956.2 DPS, again, this number would be greater now due to the extra crit chance.