Full Build on ADC's

OK, So I was no-life'ing it and watching some LCK vods and I got to wondering about late-late adc builds. I know that the current meta has a late game adc build as IE, PD, Zerkers, BT/Bork, LW, Defensive Item/Mercurials, but what about those games where you go beyond the 6 item point and can start thinking about different items? Mainly I was thinking of the Last Whisper, So I did some research and plugged things into calculators and found that an ADC (I used trist with GA) at full build, gets a roughly 30% increase in damage from getting a second PD and replacing her Last Whisper, due to the increasing returns from the AS and crit that scales with more AD where the penetration scales less so. Add in the rise of Cleavers on most AD Bruisers and a Last Whisper at the 50+ minute marks seems less efficient. You can even substitute a Bork/BT(whichever you haven't yet gotten) for the LW and receive a slightly diminished increase in damage for increased safety/kiting. This is all in theory of course and I should mention that ADC is honestly my worst role so while the math might support this, human ability and game insight might say that the increased AS/LS/Crit is only useful in a mechanically perfect environment and in a true match where you can't possibly DPS at the maximum rate the almost static increase from LW is more efficient. All insight is welcome and if anyone is/can get a high level ADC main to give me their view on this idea it would be greatly appreciated.