I think that Joe Gallo was a real gangster.
Not only had the balls to go against his boss, but when he kidnapped Magliocco and those captains including Joe Colombo didn't whacked them only because he knew that other families would kill him. When gets out of prison in 1971, the situation is different; Joe Colombo has attracted too much attention and must be whacked,Gallo in prison has made links with blacks including Leroy Burns and organized the hit.

When Gallo made a mistake ?

In 1971 for having organized the murder of Colombo he could become boss thanks to Carlo Gambino, who at the time controlled the Commission.
With the ties he had with the black criminals could give strength to the Colombo family and certainly would have renamed Gallo Family.
So he would have to act as a Sicilian, operate in the shadows and don't attract attention.