Lightbringer is an extremely good AD carry item in Dominion. Not just because of the passive, or the efficiency of the stats, but it does something very useful, which is builds out of mid-cost items very quickly.
While IE/PD may be the 'best' build in terms of single target DPS, if you fall behind the damage v defense/time curve in a game, it's difficult to farm up the money to get ahead again. Therefore, saving up for BF swords is really, really painful, and usually only efficient in the lategame.
Therefore, I really like builds that give ADC the ability to continue increasing in power as the game progresses, by building their multiplicative damage stats (AD, AS, crit chance, Apen). I find that Lightbringer/Ghostblade/Last Whisper/Executioner's Calling outperforms many IE/PD/SB builds.