Ah, it's almost "relieving" when you see, at the end of the day, that you are not the only one struggling with WebGL performance.
Feel free to DM me on Twitter (I just followed you), I'd be glad to talk about such issues, as we use pretty much use the same libraries (Pixi+TexturePacker)
Quick tip (that we forgot) - Spector can be used as a JS library, useful for mobile. Firefox and Chrome built-in became useless and removed it from latest versions.