The "you won't get big fines if you try your best" thing isn't in the law. I believe you that it is probably true, but it relies on the reasonableness of all current and future regulators. I don't like that.
By its very nature, however, you cannot nail such a thing down and define it precisely beforehand.
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.
As an outsider, I would love to hear that that's not how it works. Do the member states have any checks on each other's enforcement?