biomethane aka methane from rotting plants? extremely inefficient and requires intensive agriculture

Alternatively: captured cow farts, rotting food waste.

Remember, it is only needed for a few dozen hours a year. It doesn't need to scale.

What does it mean for a gas to be 'fickle'? Hydrogen gets stored long term all the time. It's made in refineries and used in chemical plants all over the world every day. It's expensive to store, but it's certainly doable with the right metallurgy. If your goal is reducing carbon emission as much as possible, it's way better than methane, regardless of source.