Thank you for the feedback!
You are definitely correct about lag in the browser. I think Chrome is a tiny bit better than some of the alternatives when I tested it. It does offload some work to the GPU even from the browser, though, which helps.
The hitboxes probably do need some work. :)
The inventory system is also open source and available on GitHub, as well, at: https://github.com/berubejd/GodotInventory
I implemented some functionality that you can avoid if you don’t mind that Godot offsets the sprite when you pick it up. (I didn’t care for how it looked at the time.) The GDQuest guys are working on a demo of an inventory system which uses this native drag and drop. You can also look at the official demo here: https://github.com/godotengine/godot-demo-projects/tree/master/gui/drag_and_drop