FT front-pager, but the facts underwhelm. When Ahmadinejad became president in 2005, Iran was producing 4.2mbd (million barrels per day). Now it's down to 3.8 or 3.9, which definitely costs them billions, but as a percentage drop, we're talking only 10% max. Frankly, I would expect that level of drop anyway because of Iran's wariness on using foreign technology in the first place--a bad habit of NOCs (national oil companies) everywhere. I wonder what PEMEX's drop in production has been the last five years in Mexico. Subtract PEMEX's percentage drop from Iran's and you might get a clearer sense of the delta caused by the sanctions.
Iran's bigger is also much like Mexico's or Saudi Arabia's: the domestic use of oil is growing faster than the production, narrowing the margin for export. The effect of sanctions, I would imagine, pales in comparison, even as it exacerbates the situation.
But back to Bremmer's good point in his book: state capitalism prioritizes the state over economic efficiency, so this is simply viewed as the cost of doing politics.