Just to be sure we talk on the same base, your argument only works in Frontline, while ranked Feast is a thing too. I know you talked about Frontlines only, but your overall conclusion about my suggestion leads to think the skill is ok overall. There is no such thing in Feast as Melees and Tanks having 30% dmg taken reduction (and +15%dmg inflicted).
And I talked about what other options physical ranged DPS are providing compared to Concentrate. This skill is clearly weak in almost any scenario those few dmg are unlikely to make any difference between a kill or not (even if it might technicaly happen), making it a not a worth option to bet on. Better save someone from a kill with all the other options they can get, or Heavy them so you're sure everyone can deal dmg more easily (providing more dmg then).

Edit : I played during that era of pvp, I'm not asking ranged to be as powerful as melee overall, especially in Frontline. I'm really focusing on that poor option they are given.