I don't think brief flashbacks really cover how ELEMENTALLY monstrous and evil Kratos is. He's one of the worst living things on the planet, you have to show that. You can't hide from it.
who said brief? i think you have a whole episode of flashback and other moments dotted throughout - but you want it to be a reveal what a monster he is, and his son is finding out etc... bc it is a new show
BUUUUUUT you also don't need to spend hours and hours showing him murdering and raping everyone in sight (and at a certain point, we have to admit we're in 2023 and that stuff won't have the same effect it did back then when the edgelord 2000s schlock that it was, was seen as monstrous but
cool), bc you have to believe that he can change and want him to change which is what he does over the course of the Norse saga, and the Greek games weren't made with that story in mind.
Do a full flashback episode when he gets the blades from under the house of Him brutally leading the Spartans, doing the deal with Ares for the blades, his family becoming scared of him, Murdering his wife and child. Have other flashbacks of Deimos to show the cruelty of the Gods, and brutally burning Greece to the ground in his quest for revenge including innocent people to the ground is plenty - stick to the stuff that's personal and meaningful (like TLOU) and make it very violent, brutal and tough to watch.
My point is there doesn't need to be three games worth of Greek stuff... you can get the point across much quicker without dragging down the much better Norse story.