I have been following them for a few years and they are making some slow and steady progress
From their page: As the world generates more electricity from intermittent renewable energy sources, there is a growing need for technologies which can capture and store energy during periods of low demand and release it rapidly when required.
At Gravitricity we are developing innovative, long-life, underground technologies which store energy safely and deliver it on demand at a lower lifetime cost than current alternatives.
I think Gravitricity (obligatoy, stupid name) is trying to make it more space efficient and consolidated, rather than occupying massive amounts of land.
Water also isn’t the safest thing when in massive reservoirs, nor is it all too easy to get it there in the first place.
So while you’re correct in the sense that we have GPE batteries, they aren’t super easy to build nor maintain. I think this is where [stupid name here] is trying to place themselves.