But fair enough, nobody should be trusted blindly. This is why we have appeals and legal avenues to create checks and balances. So in the context of this discussion, it's pointless. We don't have to trust them. If a fine looks disproportional, there are legal remedies. Up to the ECHR which is generally quite careful in it's decisions.
If you don't trust the EU's legal system, that's a different problem. One that rings a bit hollow, and doesn't really further the GDPR discussion.