The thing is, Chauvin wasn't some chump off the street with little knowledge and zero responsibility for his mistakes. He was a police officer who was trained to know what actions could possibly kill someone, making his actions even more egregious, which was part of the testimony of other police chiefs and officers.
In addition, bystanders in the crowd were begged Chauvin to get up, yelling that Floyd had stopped moving and wasn't breathing - all of which he ignored.
My guess: his sentence be longer than 20 years. Since the Feds are planning to get their own pound of flesh, Chauvin could wind up in the pokey for the rest of his life, which is what he deserves, IMHO.
I can't see him walking free in ten years or less. If he does, street justice will almost certainly rear its ugly head.