Incredibly disingenuous for nuclear power proponents to state that grid storage is expensive. Your entire argument centers around the most expensive power generation available and one of the slowest to build.
Grid batteries are mostly four hours duration because that's the natural charging and discharging rate for current chemistries, and there's no financial case to store energy for longer right now, as in there's no demand for long term storage at all. Four hours of storage is super profitable, eight hours is just unnecessary and nobody pays for it.
Plus, referring to this in terms of "hours" isn't exactly the most informative reference, the more underlying characteristic of storage is if it's meant for daily cycling, meaning that it makes mine every single day from arbitrage, or if it's multi day which is not a super profitable form of arbitrage at the moment. Daily cycling makes a ton of sense with solar. Longer term cycles make more sense paired with wind.
