Riot, you're going about buffing Gangplank in the wrong way.

Gangplank is struggling currently because he gets dicked on by nearly every champ in the bruiser class and nearly every bruiser is strong currently through build path and Conquerer. Riven, Jax, Darius w/ Ghost/Flash, Kled, Pantheon (sleeper OP right now), Jayce...champions like these beat Gangplank into the dirty early and seeing as games snowball pretty hard and don't last until "4 item with lvl 13 barrels Holy Mecca of GP" nearly as often, you don't get to farm it out to comeback nearly as often.

Gangplank doesn't need more bonus damage to champs on his barrels and he doesn't need more damage per wave on his ultimate. Quite simply, Gangplank doesn't suffer because of lack of damage in his kit. He suffers because you guys dicked him so fucking hard on the patch where you reduced his barrel time from 60 seconds to 25 seconds (good nerf), increased his lvl 1 Q mana cost from 40 to 60 (brutal nerf), and made it so barrels don't grant temporary vision (unnecessary nerf).

I can see the reasoning behind increasing his Q mana cost because you don't want Gangplank oppressively spamming Q enhanced by either Grasp procs or Klepto procs while Corruption Pot is burning. So my solution to that issue is to refund a flat 20 mana on kill. That way, players still have to decide if they want to spam it on their lane opponent at 60 mana per Q, or they can actually use their Q to farm a little safer. Gangplank has a base mana pool of 282 so at 60 mana per Q he runs out incredibly fast. That is why that mana cost increase was so brutal.

All in all, I think Gangplank is in a relatively decent spot, he just needs love to his early laning phase through mana cost buffs/refund mechanic applied to his Q. His W costs a lot and has a high CD as it should with such a powerful ability. I get that he should in fact suffer to his biggest lane counters (Pantheon, Jayce, Darius with Ghost/Flash..etc) but you shouldn't run OOM after 5 Q's and then run the risk of getting murdered just for trying to farm at melee range. Even when you do forgo trying to contest minions and farm and just play safe with your mana consumption, you are incredibly easy to tower dive due to no escapes and no real outplay potential outside of the surprise Orange if you have the mana for it.