Re: relying on third-party services
"the EU has been unable to provide an effective shield for companies to trade with Iran in the face of US sanctions"
I'd say more "unwilling" than "unable". If the EU was prepared to bear the consequences, it could prohibit complying with the relevant US rules.
They're obviously unwilling because there would be severe disruption (assuming the US didn't give in to avoid losing the business) until/unless EU equivalents replaced the US institutions - imagine Mastercard, Visa, and every bank that can't do without the USA simultaneously withdrawing from the EU.