Why are we nerfing Kog'Maw again?

So, there's this PBE update, where they are "tweaking" Kog'Maws W (Bio arcane barrage). It's a steroid which currently deals 1.25% Max HP per 100 AD, and it's being switched to deal 2% Max HP (with no scaling) which is, actually a significant nerf, when we consider Kog'Maw is at an all-time low, with games being too short for him, itemization being awkward for an ADC that doesn't get a lot from crit and so son.

"Buy hey mate, isn't it a buff to his early game?" It's actually not a buff to the early game and here's why: Kog'maws %HP damage is completely irrelevant in the early game, it's a tank-shredding tool, but early on, tanks aren't really tanky, and he doesn't have (yet) the AS to capitalize on his steroid (2% Max HP on a typical midgame 1400 health tanky target is 28 damage before resistances, that's... kinda miserable). So the change, while being extremely heavy as a nerf in the lategame (Kog'Maw on the typical Guinsoos + BotrK build is hitting the breaking point as soon as lvl 12, and from then on it's only nerfs, and that's if he builds 0 AD aside from those two items, which we know is a bit of a waste, and not even taking into account the guinsoos rage buff) does literally NOTHING for him on the early game.

But this isn't outrageous because we're nerfing Kog'Maw, it's outrageous because we're nerfing the WEAKEST ADC AT THE MOMENT (barring Urgot who somehow managed to become WORSE after preseason item changes) in what kind of world does nerfing the weakest ADC even make sense? Not to mention, aside from poor old Kog'Maw, most on-hit champions are on the broken side of things right now (Looking at you Jax) soo there's a HUGE chance his main items and masteries (Guinsoos and Fervor) will be nerfed to the ground in the future, why are we doing this again?.