Not sure about that quote; I did read Accardo started out as McGurn's (real name Vincenzo Ribaldi) driver. McGurn of course was eventually gunned down himself, likely on Nitti's orders. He didn't have much to offer the Outfit after Capone went to prison, his only real skill was killing people, and he was apparently putting up a stink about being tossed out to the point of saying stuff like "I know a lot of things about you people." He was gunned down in a building that was then a bowling alley and is still standing on Chicago and Milwaukee. Then of course Geraldo famously interviewed his then-girlfiriend, Louise Rolfe, aka, the Blond Alibi, in the 90s, and she maintained McGurn had nothing to do with the massacre while conceding that he might have planned it. But she maintained they really had been holed up in a hotel when it went down.

In Russo's book he basically writes 500 pages on Humphries without ever mentioning if he had a title.

I would guess he was below only Ricca and Accardo in terms of formal status and in terms of actual power, probably their equal or superior, if Russo was in fact correct of his characterization of Humphreys as being the operator responsible for nearly every notable thing they did post-Capone.

What I am saying is, the way Russo characterized it was like saying well, there's one guy on this plane who knows how to fly it. It really doesn't matter if you call the flight attendant the captain, there is still only one person who can fly it and that is all anyone cares about.

But Russo's book might have gone a little over the top in its admiration of Humphreys.