I don't know the particulars of gravity storage, but had heard it wasn't very impressive. Industrial sized molten salt batteries seemed to hold much more promise. But yes, the only advantage to hydrogen is that it can be quickly pumped. Which makes it much more useful for vehicles than any other storage medium. Batteries have to be replaced, contain dangerous chemicals, and charge very slowly. The only real option for batteries is to switch them out at replacement stations. The energy losses in hydrogen seem small to me compared to issues with batteries.