The first Thor fight literally ended with him getting punched full force in the mouth, once he had sufficiently pissed Kratos off by threatening his son and going "THERE he is, there's the God of War."
Norse Kratos isn't WEAKER than Greek Kratos, he just holds back most of the time unless he has reason not to, such as with Baldur, Thor, Heimdall, Odin etc. Because he DOESN'T want to destroy another world on a blood soaked rampage, which is fair enough quite frankly.
Greek GoW is more hax, Norse GoW by all accounts is at least as strong if not stronger, regardless of how toned down the spectacle is.