So basically what you're telling me is that since they aren't a middle eastern country, we should keep pounding them more and more into the earth economically then they already are. But it's completely okay to show economic mercy to these countries who would gladly take the money and run when they get the chance to?
I mean, my political knowledge is pretty mundane, but Russia has been in economic shambles since the early 80's when we were just getting finished with the Cold War. They spent too much into their military budget, with none of the major western powers properly, financially backing them. So when it came time that their entire facade of competition was to fall apart, they gave in and ended the stupid conflict that dug themselves deep into the hole that the early Cold War started digging for them. So now we've reached the second Cold War with even more sanctions and conflict between Russian/Eastern Powers and Western Powers. However, your focus seems to be completely tearing down on and beating up Russia.
This is an understandable standpoint if you're missing a couple key facts. First, we didn't offer 'economic mercy' to Iran, we made a deal with them to gain something we wanted. Iran's economy has been devastated by sanctions imposed by the US and the rest of the Western world for decades - they wanted those removed. The US views nuclear non-proliferation as part of our national security, so we wanted to make sure Iran wouldn't gain nuclear arms. The deal did an excellent job at it - without going into specifics, the provisions of the Iran nuclear deal brutally crippled any chance that Iran had at creating nukes.
Second, Russia's economic situation is complicated. The thing in the 80s that you're referring to was basically the complete collapse of the USSR. Russia isn't even run by the same government that ran the country then. Also, Russia is a world economic power. They rank 11th in nominal GDP (whereas Iran ranks 27th). Our sanctions are objectively
more crippling to Iran than Russia because Russia has vast oil wealth, predominantly doesn't trade with just the US, and can withstand heavy sanctions. So if the issue here is, "why are we being so nice to Iran and so mean to Russia," the situation is more or less the opposite of that. We sunk Iran into deep poverty by cutting them off from the rest of the world. Russia is relatively wealthy even by global standards.
Iran didn't 'get away' with anything - they agreed to sacrifice their quest towards becoming a nuclear power, and in return we offered them an in back into the world economy. Despite the fact that Annoying Orange has set US sanctions back into motion, there's 5 other major EU countries that are still on the deal - it's wholly possible that the deal will still last even without the US in it.