This was always an overboard sentencing to make an example of an arrogant man who refused to snitch.
The message from the DoJ to everyone else was, "If you do not cooperate with us because you'd rather take your lumps than be a rat, we are going to really put the boots to you. Don't be a Jimmy Dimora, be a Frank Russo.".
If I added it all up, I've spent months in the '90s working at the private homes of influential people, while my payroll hours were recorded as if I was on some big commercial job. Everyone does "the Leona Helmsley", so-called top secret "government jobs", trading favors. It's only prosecuted when they want to throw someone out of the club. I know of 2 trim carpenters that spent probably a total of 15 wage-months out of 10 calendar months trimming out a new mansion, while the IRS thinks they were working (inefficiently!) at a new nursing home and a hospital. This happens all of the time, with no consequences.