Easiest/Fairest way to Nerf GP, coming from a GP main

I know a lot of you are now starting have issues with Gangplank. No doubt, he's a very strong and hard scaling champion. He's meant to be a late game monster. I think the best way to safely nerf him is to increase his Q cooldown, or increase its mana cost so it can't be carelessly used for harass. GPs kit is already a shadow of itself after he was reworked. His barrels and gold income have nerfed massively as compared to what it was. But GP mains will always find a way to manage. While its best to start with nerfing his Q, it would also be a good idea to adjust or mitigate his bonus gold income. Again, GP is meant to be a late game champion, and I think it's best to nerf him in such a way that makes it take more skill for the player to reach that point.