Wait... where do I complain about windwall? I'm confused.
Secondly - sure gp orange costs a bit of mana, but you also don't need to go doran blade, longsword, or doran shield or cloth armor like most people top. Second, you get 1.5% mana back via masteries. Thirdly, you only need mana for oranges and q harass which is more or less completely regenerated thanks to it's low cost and you being able to start mana item and the 1.5% mana back. Meaning - you only run out of mana if you spam oranges non-stop on cd. Barrels are literally free. Also, you never do a face-to-face trade as gp unless you know you will win - you play like pantheon and spam q from range... so that when you do have a face-to-face trade, even when the other guy wins the damage trade, you are even or ahead due to q ranged harass. Which btw let's you get a shit ton of gold cuz it counts as a melee - instead of only giving the smaller sum of gold for being ranged, it gives the full melee value. Combo this with gp's natural extra gold income and just trading farm means gp always gets more gold. So because people can clear his barrels from range and one champ can do it aoe if they perfectly line up their aoe aa we need to nerf that champ? No. That's just a gp player being a little crybaby.
Gnar is intended to counter melee champs - like all melee champs without spammable ranged harass (gp, panth). And gp wasn't intended for mid so uh... kinda same story as your argument for gnar vs renekton. Also, azir doesn't invalidate gp's strength at his supposed strongest point in the game while also being much stronger than him at every other point in the game. But that's exactly what gnar does to renekton. Thus, there is a champ imbalance in the latter case and something ACTUALLY NEEDING FIXING whereas your complaint is a mere inconvenience. And yet you don't see boards flooded with "buff renekton" posts or whatnot. Meaning basically you have no strength behind your argument. Sure it's annoying, but it's not something that demands fixing nor makes gp unplayable, nor invalidates him as a champ just because azir is in the game. Also... lucian or ezreal mid? They can aa probably 10x easier than azir and clear gp barrels to deny you and both are viable mid. And then there's always vayne or quinn top. But I suppose "that's part of the game"? Well, congrats, a skilled azir can do it while farming. So he's playing "the game" too. Get over yourself.