I think this "debate" is largely irrelevant: China has decided that locomotion will be (battery) electric. That is the largest scale you can get, so any effects of scale for an alternative will at best be as large as the battery electric one.

And then there are the variety of other disadvantages that come with hydrogen: - significant leakage and high greenhouse factor - heavy support equipment need (both for storage and for usage)

About the only advantage of hydrogen (vs. lithium-ion batteries) is gravimetric energy density (where it's about a factor of 300). But even volumetric energy density differs only be a factor of 5-10. (Both numbers ignore that the storage thing will add significant weight). And those are _already_ not limiting for locomotion needs.

- how sure are we that we are solving a co2 climate crisis with the actions we are taking?

The thing here is yes: Even if we would generate the energy for the locomotion completely with fossil fuel! Large plants are significantly more efficient (10-35% vs up to 60%) and it would be _much_ simpler to, e.g. think about carbon capture if we had tens of thousand CO2 emitters rather than a billion. But we are not doing that!