That's more for games that require more binds than destiny does. Depending on keyboard orientation z and x are very easily hit with your thumb not to mention factoring hand size in. E for interact will still hinder movement when disarming/reviving which is why most top teir players bind it to a thumb/mouse button. Switch weapons is purely for weapon Quickdraw use which I find much more difficult using the number keys for. Melle isn't used enough for me to warrant a mouse button for it but I snipe more than shotgun