I'm confused. I used to main GP, and I'm going to be maining him again because of how huge this buff was. You guys don't seem to understand his ult. It isn't a giant death nuke. It is a global zone denial tool, global wave clear tool, and anti-all in tool. It isn't supposed to be a massive damage threat. He isn't Ziggs.
If the enemy top laner goes all in on you, drop it on yourself and either win the duel because 500+ damage is an absurd amount if they fight inside of it for the duration or just back off through it, fighting as you go. If the bot lane is getting ganked, drop it on them to make sure the enemy bot lane and jungler have to go through the whole length of the nuke and slow to finish them off. Oh, you're team fighting at Dragon and the enemy is split pushing top? Clear the wave top. Enemy is disengaging a fight? Drop it behind them.
His ult isn't for putting on top of the enemies head and having them die. It never has been. It is for putting on top of their head and having them be forced to get out of the zone. Which is exactly what they are doing if they are running away immediately and only getting hit by it twice.
Sure, I'll take a buff to his ult. But he really doesn't need it.