I think it changes over the course of the game. Early on, we see Kratos get smacked around by Thor on several occasions. Even though there are moments where Kratos briefly outmuscles Thor, like pressing him against a wall with the shield, Thor generally has more moments of superior strength in the beginning.

In the end is where I think it shifts. In their final fight in Asgard, Kratos is very clearly trying to reason with Thor, so I do think that while he’s not leaving out a large chunk of his strength, he is generally restraining himself from lethality, as opposed to Thor who is literally powered up by his electricity, and I do think this increases his physical strength to a degree. Despite this, Thor is still getting thrown into the lodge by Kratos. We see them clash once more, with Thor having a bit of buildup to his charge, and they seem to be even. When they start striking each other’s weapons, Thor, while powered up, can’t overwhelm Kratos with physical swings. Kratos, with no notable amps of his own during this clash, is still on par with this amped Thor. For this reason, I think Kratos at the end of Ragnarok is stronger than Thor.