Incendiary Airbust Launcher direct impact

Dealing damage with the Incendiary Airburst Launcher as Support only works if you directly impact an enemy player with the projectile. I have killed many enemy players with the AOE damage and I have seen zero progression. I am currentely sitting at 158/2000 damage after getting multiple double kills/triple kills with the launcher. Im not sure if this is intended, but it makes this challenge a ridiculous grind.