Initial impression on the Koggy W change
I'll start by saying I'm a Dominion player, not a Rift player, so my insight might not transfer over.
The change to Koggy's W has gone a long way toward patching up his lacking early game. Previously I would start with a pickaxe and just bum-rush Rageblade, completing it at around the 4-5 minute mark. I would be more or less useless until it was finished. Now I can safely start with Recurve+boots and present a reasonable threat to the enemy team early game.
With Rageblade and Mallet as my only real sources of AD, the change to W's scaling has relatively little late game impact on my build. I've lost about 0.5% HP damage late game.
Koggy's Ult-focused AD builds, however, have taken significant nerfs as a result of the W changes. If Riot finds that Kog is still under-performing, I would suggest bumping up the bonus AD ratio on Koggy's Ult to make builds centered around it a bit more attractive. It would be a shame if OnHit builds are the only workable way to play Kog.
Overall, the change to W feels like a decent buff to TanKoggy's early game and an all-around buff to AP Marksmen Kog. It's a nerf to any build that relied heavily on attack damage to get 4% HP Ws and nuclear bomb Ults.
I give this change
Kogs out of five. The direction is fine, but it still needs some tuning.