There’s a certain terrifying symmetry about the fact that the Doctor started and ended the Time War committing genocide.
Those who watched The Day of the Doctor and said that of course the Doctor would find a way to end the Time War without wiping out the Daleks and the Time Lords have a rather selective view of just what some incarnations of the Doctor have been capable of.
Also a good reminder that Seven’s both adorable and a manipulative, ruthless bastard. My own personal head-cannon is that the Doctor waited so long before returning for the Hand of Omega because after the First Doctor, there hadn’t been a regeneration which had been enough of a cold-blooded so-and-so that they’d consider using it as a weapon. Let’s not forget that One was the adorable, giggly old man who in his first appearance attempted to smash a wounded enemy’s skull in with a rock.
^This. there is a difference between how the Doctor would prefer things go and what he is capable of. And the capable depends on the regeneration.