There are significant issues that limit the scalability of these systems in terms of power, capacity, and duration.

Building larger heat storage capacity, for example, would be useless if it cools down before being used. Long-term storage is an area of active research. There is reason to believe[1] that the technology could improve in the future, but until that is proven to be viable the state of the art for duration is "a few hours".

Speculation doesn't keep the lights on. The grid can only be powered by things that actually work in the present.

[1] https://spectrum.ieee.org/long-term-energy-storage-molten-sa...