What makes you think that the top player is trag? I'm not saying you're wrong - I can't see what gear he was wearing when he did the 121 clear but currently he's using pestilence with mostly level 130 augments.
I definitely agree that the status quo builds should be challenged. I haven't tried trags much myself.
From my understanding, ignoring other multipliers:
Trags fires a 1750% weapon dmg lance + a 525% lance from you, both receiving 3,300% dmg. This means around 75,000 * weapon damage. It also provides toughness from healing and blood rush runes.
Pestilence fires a 1,750% lance and another from consuming the corpse. These receive 1,650% boost from pestilence set. That's 57,000 * weapon damage. Some toughness is given from the 4 set bonus too.
Based on that alone, trag does more damage.. but pestilence allows you to take brittle touch rune, skip all CHC on gear, allowing you to prioritise attack speed, crit damage and CDR, while still having 100% crit chance on important fights. They're very similar builds and probably compete well. Trag may win with imperfect gear but I think at the absolute max/min level, pestilence wins out due to the gear optimisation and crit rune.