A hydro-driven grid does not need storage. Hell, if you have enough hydro, it can even be your storage. Not all of Europe has the geography to be able to cover their needs with just hydro.
If Germany was willing to build new nuclear power plants I'd be potentially in favour, but it's not going to to happen, so H2 will likely be the way, and it won't be cheap.
That said, I also invite you to go look at cost estimates for batteries from just 5 years ago and compare them to today, or solar / wind cost estimates from 15 years ago. Those technologies have experienced significant reductions in cost due to scale and industrial learning.
IMO the biggest problem with H2 is that similar sorts of learning / scaling processes simply won't even start until the grid evolves to a point where the seasonal demand shifting is actually required, but by then it's essentially too late. And there's not really any hope of governments kickstarting the learning process with artificial demand because people will make all sorts convincing arguments for why it's a stupid waste.
So I guess we'll see what happens. Perhaps stuff like fertilizer and steel will help the technology matures before the grid needs it, or perhaps battery technology will surprise us again, or someone will figure out how to make flow batteries work or whatever. I'm not particularly confident in any of these technologies, but we'll just have to wait and see what happens I guess.
Something *does* need to be done about storage though, even with all the complementary wind-solar and giant Lithium or Sodium battery installations, and all the HVDC you could want.
If you were to have an environment in which H2 would actually make economic sense, non-H2 storage and distribution systems would be even cheaper, and they can be added incrementally rather than needing a big bang, preventing investing in H2 from taking off in the first place.