> I'm highly skeptical that a battery + inverter (w/o solar), using time-of-use for payback would ever make pure financial sense.

Ever? Batteries are 10x cheaper today than they were ~a decade ago. If that trend continues for even a little longer, they'll be absolute no-brainer like solar is today within the next 5 years.

2026 seems to be roughly the break-even point. And whether it's worth it depends on where you live (greatly affects the cost of both installing a system, and buying energy from the grid).