Both, plus another additional reason.
Fallen God Kratos was confirmed verbatim to be weaker than his peak GOW3 self by
Bruno himself because of his stab wound that he had to then heal from and due to his lack of sleep, this same Kratos then fell out of training and slacked out massively to the point where we see him in 2018, where the novel ultimately confirms that Kratos atrophied massively and was indeed more muscular in his early Greek days. Remember, he tried to starve himself to death and walk endlessly to no avail, he couldn't even die from hunger if he wanted to, he only ate at this point to satisfy his taste buds.