No one is storing 1000C water at home.
It is true that the temperature deltas affects efficiency. You can use the thermocline to draw from the cooler lower portion of the storage tank to push this further. Or less technically, just a bigger tank, though this has some tradeoffs.
In warmer countries they are set up differently can act as free air conditioning by extracting heat from indoor air at the same time as heating water.
Right, but UK has/had "storage heaters" which were bricks with nichrome wire. They would heat the bricks really hot during cheap electricity times, and use that heat the rest of the day.
EDIT: I misread "ripping out these energy storage devices" as https://en.wikipedia.org/wiki/Storage_heater
Of course heat pumps for DHW should all have a tank for smoothing demand across several hours.