Talking about PUBG mobile. The audio experience while playing pubg on Asus 5z is on another level. 6Z should have incorporated that.For #5, Android system will utilize available RAM to enhance the performance. Since ZenFone 6 has larger RAM, system will use every bit of it to make the performance better. I don't think you should worry about it.
For #6, could you provide the name of the game? We'll compare it on our side.