Energy storage is viable and being deployed right now. Moss Landing California has one of the larger installs in the near future, at more than 1 GWh, because it's cheaper than gas peakers.
Recent bids for solar/wind attached to storage are coming in at record braking prices in Colorado, Nevada, and Indiana. Every month there are "record breaking" bids for storage projects, today's news is about Hawaii:
But in a few weeks there will be a new low cost somewhere.
Batteries are getting cheaper faster than anybody expected, just like solar and wind did before. Fusion is progressing more slowly than anyone imagined, and will likely never be financially competitive. Nobody even talks about it being cheap anymore when I ask people why they think fusion is exciting. At best we're getting simplified supply chains, or baseload power. Even baseload power is not desirable, coal plants are shutting down all over.
And in addition to all the grid storage that will be added, people with electric cars will keep 3 days worth of their own electricity in their garages at night. Huge amounts of storage will be deployed by the EV switch, and as those batteries age out they can have second lives as grid storage, before finally being recycled.
I believe battery tech is progression slower than fusion. We will also need a clean baseline power solution, and AFAIK only fusion can give us that.