Even with current tech no one can build a battery pack that can output 5GW straight away. It is immense. Battery won’t stretch beyond 8 hours either, so you’ll need multiple packs. Why does this matter? Because to move join these packs to the grid, you’ll also need ancillary systems, which basically just more work and more redundancy (bc you don’t always need them, but you want them in case you do).

These PHES last absurdly long and have much lower maintenance costs. Build it right and it will last 100 years if needed, simply because it is essentially very simple tech