Gangplank main here, you completely lost me on the removal of Remove Scurvy. I'm sorry for my French, but Walk the Plank is RETARDED. Your reasoning is BULLSHIT. Twisted Fate Gold Cards? UWOTM8? Have you forgotten Morgana? You know, the bot lane terror that has a "my team reported me for AFK" 3 second long snare that doesn't seem to be going anywhere anytime soon? What about Enchanted Crystal Arrow? Ahri's Charm? Fiddlesticks' Terror? All of these abilities have HUGE durations of complete loss of control, and Gangplank stands out from any of the other champions because of this.
ult? Eat oranges and be k.
ult? Eat oranges and be k.
wither? Eat oranges and be k.
Gangplank doesn't need a gap closer because he has Remove Scurvy. You flat out said that you're keeping Grog Soaked Blade and are BUFFING it. Why the fuck would he need a gap closer when he can slow any champions whose names aren't Evelynn, Master Yi, and Olaf with constant ranged harass, and if they use crowd control to disengage, you eat oranges and be K. Worst case scenario you pop your ult to cut off your opponent's escape route. Of course, there'd be nothing stopping Gangplank from building TriEdgeGhostblade to just cheese your enemies with 1600 Parrrley damage, but I've thought ahead of that.
How about instead of nerfing Parrley's range, you gut it's damage. And for each stack of Grog-Soaked blade on the target, they take 1.2 - 2% of their missing health on Parrley hit. It's meant to be his bread and butter farm ability, and the thing that makes Gangplank the pimp daddy of top lane. Gangplank ain't meant to scale hard, he's meant to scale fast. He doesn't get to do 500 bonus damage endgame like Nasus, because he uses the gold to put himself far ahead in terms of itemization, not a ball of stats.
This is the direction I want Gangplank to go in. This is how you keep his identity without turning him into the 1600 damage Q wonder he is today. This is how you make him balanced, without having to remove his identity as the AD caster duelist hybrid he is now.