Gankplank's early game shouldn't be so safe
As a late-game hypercarry with as much utility and damage as he has, Gangplank's early game needs to be a risk. The problem with his early game is that it's way too safe. In bad matchups, he just farms with Q and wave-clears with Barrels. In good matchups, he dominates the lane because his damage output is still pretty high.
You can't push to his tower because he's good at last hitting, you can't freeze the lane because his last hitting is ranged, and you can't let him push because he can just chunk you under the tower with Barrels. He's also difficult to gank because of his Oranges and speed-boost.
And because he scales into such a late game monster, it's kinda important to abuse his early game. Because of this, he can't be allowed to play as safe and comfortable as he currently does. People should be worried about picking Gangplank into Renekton or Riven because they risk getting demolished. As of now, any Gangplank player can just farm safely with Q, disengage with W, poke with E, and get fed across the map with R.
My suggestion would be looking into his Q or W. I think lowering the amount of gold he gets from Q farming would be a good place to start, same with lowering the heal he gets from W. But that's just my 2 cents.