I think that they have been a little less violent in the seasons after the 4th
In the nine episode span of "Season 6, Part II", there eleven murders, 8 of which are mob hits. The pattern of each season is a violent end. Examples....
Season 1 : Mikey Palmice, Chucky Signore, and Jimmy Alteri are murdered
Season 2 : Matt Bevilanqua, Richie Aprile, and Big Pussy are Murdered
Season 3 : Sunshine, Carlo Renzi, Dino Zerelli, and Jackie Jr. are murdered.
Season 4 : The hitmen assigned to whack Carmine Sr. are murdered.
Season 5 : Billy Leotardo, Adriana La Cerva, and Tony Blundetto are murdered.
Season 6 : Vito and Fat Dom are murdered.
Season 7 : Christopher, Burt Gervasi, the Russians, Bobby Bacala, and Phil Leotardo are murdered.