The single time I've ever had an issue with the IRS - I forgot to sign a 1080X - They sent me a letter, I signed it, and everything was perfectly fine. They collect a massive amount of payments and paperwork every year. I don't know how you could say they're barely functioning.
The DMV on the other hand is the joke in American culture about incompetent bureaucracies.
Count yourself very lucky that you never had an issue with the IRS. I had to deal with a mistake that the IRS made erroneously and even after 4 years it is still not resolved. Every 6 months I get a letter that the IRS still hasn't bothered to look into it and I'm guessing they likely never will.
DMV is the butt of all the jokes, but atleast you can walk into a DMV office and a real person, however annoyed they might be will try to help you.
The DMV on the other hand is the joke in American culture about incompetent bureaucracies.