For long term storage, capex is king, not round trip efficiency. The capex of batteries ($ per kWh of storage) is much too high. There aren't enough charge/discharge cycles to amortize that capex. This is unlike with diurnal storage, where there are many thousands of cycles over which to spread that cost.

Thank you that makes a lot of sense.

To go into more detail: you want to really aggressively minimize capex, even at the expense of round trip efficiency, for long duration (like, seasonal) storage. The interesting example from Standard Thermal is something that could reach a capex of $0.10 per kWh-th of storage capacity (yielding heat at 600 C). This is three orders of magnitude better than batteries. Even tossing in 40% round trip efficiency from converting this back to electricity using steam turbines it would be vastly superior to batteries for seasonal grid storage.

There are varieties of batteries with somewhat lower capex and lower charge/discharge rates. Form Energy's iron batteries are of this kind. They would occupy an intermediate timescale, perhaps ~1 week, which could be good for leveling wind output.

The problem with batteries for long-term storage is the capacity. You would need an ENORMOUS amount of them to store months worth of energy.