>whereas most experts I heard from propose to use hydrogen (or methane) as a storage medium
What experts? Power to gas has been really energy inefficient with little sign of improving from what I know. It can't really compete with pumped hydro even where pumped hydro makes less to no sense it seems.
Efficiency (almost) doesn't matter. Cost and scalability matters. Pumped hydro and batteries are wonderfully efficient, but they're a lot more difficult to scale than infrastructure for storing, transporting, and burning a gas.
What experts? Power to gas has been really energy inefficient with little sign of improving from what I know. It can't really compete with pumped hydro even where pumped hydro makes less to no sense it seems.