The Front Boss wasn't all that risky until the FBI came to town.......maybe a little earlier. Ricca and Accardo were very crafty/cunning. They were going to stay in the background to reduce their odds of getting caught up in legal proceedings. All these guys had legal problems, but Ricca & Accardo stayed out of the day-to-day operations and in doing so, we're able to avoid numerous indictments. Just look at what happened to Giancana and subsequent bosses.

Absolutely agree with you about Prio. The guy had money coming from everywhere, and he was in some ways as powerful as the other upper echelon bosses. He just wasn't starved for attention and spent his time making money.
Smart man.

This is a really good bio of Prio. He was a top heavyweight in the Outfit, but did a good job, considering his chosen profession, of staying under the radar.