As somebody who has two really good plague zaw rivens. You're wrong.

Yes, my Plague zaws are my most used weapons, because I like pole arms and staffs, but to say the galatine doesn't come close is grossly inaccurate. A good Galatine build will cause it to crit for over 500k/hit with only a 20 hit combo multiplier. With a very nice attack speed buff and that's without a riven and it has stupid long range even when compared to plague zaws. Galatine, Lesion, Plague Zaws, are all some of the best weapons in the game and are VERY comparable.

Spend ten minutes online watching top ten videos from the biggest build makers on youtube. The galatine prime will be on EVERY list.