I don't disagree with any particulars of your analysis except one omission: powerwalls compete with electric cars for relatively scarce high-tech batteries. It is globally optimal for the time being for those batteries to all be used to electrify transportation, while utility power can be enhanced with large, fixed installations using whatever kind of battery they can get. Lead-acid or anything else, it doesn't really matter. But nobody is selling turn-key residential power packs using anything but lithium-ion batteries.