RE: dismembering Skull Face:
Kaz took the lead on that one, if you don't pull the trigger yourself. He guides Venom's hand and compels Venom to shoot. But it's kind of a moot point since the whole idea is Venom changes from that point forward. After Skull Face is dead, he sees his "ghost" on Mother Base. And from Paz's "ghost" he rethinks the line of revenge altogether. "You can kill Skull Face, murder Huey, slaughter Zero... Burn the whole world down, and it still won't bring me back. Me, or any of the dead. ... There's more to remember than hatred and rage." And I think that is meant to inform his arc, showing a change in him.
Venom was always slow to anger from the start. Upon rescuing Kaz he says to focus on the future rather than dwelling on the past. Upon sparing Quiet, he finds himself repeatedly at odds with Kaz's bloodlust. Things like this add up to paint Venom as a rather chill dude. Kaz thrives on anger, but it just seems to suck the wind out of Venom. When Venom does something vengeful or inhumane, it's usually his passive personality acquiescing to his assertive subcommanders. Although he does stand up to them more and more.