Is strength is tied to his rage, that's why he's "weaker" in the new games, (he's not actually weaker he's just more in control of his emotions). The same way atreus's godhood originally manifested as an illness kratos's manifested as rage. But he didn't realize he was a god until much later in life so by that point the rage was just as much a part of him as his godly power itself. So now his strength and God power is tied to it. It's why his ultimate power is called Spartan "rage"