Five years ago batteries weren’t anywhere near grid scale either. Arguably they still aren’t. That doesn’t mean we should not consider them when talking snot the grid in 2040.
Sure. But we also shouldn't assume they will be successful at grid-scale either. Planning a grid assuming that some future storage technology will be a silver bullet that solves grid storage is a massive gamble.
Hydroelectric storage is the only grid-scale energy storage system available to us, and it's geographically dependent. And the places that are suitable for hydroelectric storage usually don't need it because they can just generate electricity via hydropower anyway. Until your hypothetical breakthrough in power-to-gas or giant flywheels actually happens, this is the state of grid storage.
It's not such a massive gamble if you can just keep relying on natural gas peaker plants in case storage is somehow unsolvable, which seems quite unlikely given that we have a dozen completely different technologies for storage in the pipeline.
Hydroelectric storage is the only grid-scale energy storage system available to us, and it's geographically dependent. And the places that are suitable for hydroelectric storage usually don't need it because they can just generate electricity via hydropower anyway. Until your hypothetical breakthrough in power-to-gas or giant flywheels actually happens, this is the state of grid storage.