The law only says regulators should think about your intentions when assessing penalties (among many other factors).

Is there anything stopping a regulator from deciding an unintentional violation is "only" a company-destroying 5M euro fine instead of the full 10M? In fact, couldn't it still be a 10M fine? Or should I expect to be let off with a warning? Seems like I'm depending on the good will of the regulators of every single EU member state...

I do not think it's impossible to write a law that says fines for minor and unintentional violations are limited by statue.