Odds are the inverter will last longer than the average geyser. The solar panels definitely will. For long term running costs, you are probably right that such a separation of concerns, even if definitely not optimal, makes some sense. I would still file this under “bang for buck”… just with a more long term component.
I’ve often said that efficiency doesn’t always matter. If the energy is plentiful and there are no other constraints (such as the cost of PV panels, or the roof space), you might not care how efficient it is. Even a black pipe coiled on the roof makes hot water… not very efficiently, but for some applications you don’t care.