For a dps player, Battlemaster is close enough to Columi as long as you get 2 "boundless ages" relics (they add +206 power). The only thing you're missing out on is health.
I did an AskMrRobot workup:
Full Columi Eliminator set:
Full Battlemaster Eliminator set:
I'd bring a Battlemaster-geared dps to an op as long as they were on voice chat and knew what they were doing.
I wouldn't however, bring a Battlemaster-geared tank, that's a different story.
Just want to check if you're using PvP relics for BOTH gear sets or just the Battlemaster one as that will skew your stats.