"The planned battery would dwarf a 19 GW lithium-ion project in the UAE..."
Iron-air batteries have a 0.01C charge/discharge rate.
The reason 300MW has 30GWH of storage is because of that.
The cost per kWh (capacity) is frequently touted as the reason for their use, but in fact, you're paying for storage you'll rarely (if ever) use. Yes, it will sustain a four day outage, then potentially be exhausted the next day because it takes nearly six days to recharge (using the 0.7 efficiency). And while getting there, 60GWH of energy will be lost as waste heat.
LFP can have a C rate up to 10. 1 to 3 is common, So 100 to 1,000 times faster charge/discharge. Stack the energy behind the inverter that you actually need and spend less in the long run, both CAPEX and OPEX.
Then stack as many cells as you need to get the duration desired.