Hydro is great, except for a few problems. The biggest is that they are causing extinction for several species. The second biggest in central and northern Europe is that hydro is already used in every place where its reasonable to build them, with practically no space to further expansion.

Right before the last rush to build nuclear, Europe went through an energy crisis where they did also use reverse hydro. In recent time there has been discussion to modernize and reuse those old installations, but the issue is costs. Buying energy to sell it later, while maintaining and operating the hydro power plants and pumps are not cheap (not to mention building out transmission). Even at current fossil fuel prices, natural gas and oil is cheaper and thus reverse hydro is not economical viable.

Hydro is not renewable when the basins are being refilled by glacial melt as is the case for most of Europe, and precipitation is also becoming more erratic. For example, Iceland is currently relying on hydro power for 70% of its electricity, but current models predict that glacial runoff will peak around 2060 (or earlier, if the arctic temperature continues its upward trend). After that, the potential power to be generated from hydro will gradually decrease, which is why Iceland is now diversifying towards geothermal and wind.

Won't climate change lead to more droughts making hydro less stable in the future?

Countries who can do hydro are pretty much doing as much of it as they can. Like... there really isn't much room to increase hydro unless you start inundating valleys.

Ok... but now we're damaging ecosystems by installing hydroelectric power stations and dams and such in these areas.

Besides, not every country can effectively utilize hydroelectric power.

Germany, like other countries, should be investing in a mix of power sources. You probably want your backbone to be nuclear and then renewables where it makes sense with a goal (at least in western countries) of also eliminating reliance on China for renewables/batteries.

Dogmatism about renewables is self-defeating.

Renewables and batteries are great for peaks though. And not very good for base load

Nuclear is great for base load, not great for peaks

Our current situation is we are building tons of renewables and storage but still burning tons of fossil fuels because they cannot replace the base load very effectively. Nuclear replaces the carbon part of the equation