Just before sleep I had a long thought about Kratos and his psyche when he fights and how that correlates to his performance and experience.
Perhaps this will explain how a fight looks from outside to us players and how a fight looks to Kratos himself in levels of difficulty.
From my observation there are 3-4 general states of mind Kratos displays in fights.
1) The one where he is fighting someone he doesn't want to kill and is neither willing to defeat. Kratos doesn't mind getting clobbered to death or incapitation, he just being a punching bag in an effort to be merciful to his opponent. Any combat done by Kratos more out of reluctance and habit rather than actual malice or determination.
Case in point Diemos from Ghost of Sparta. Diemos stomped and incapacitated Kratos damn near crippling or killing him.
But then we go to Thanatos fight and something interesting happens, Diemos gets killed by single wall smash while Kratos has survived multiple wall bash combos almost unscathed. The actual difference in power here is considerable.
2) Then comes the part where Kratos is willing to defeat or but not willing to kill.
Case in point Kratos vs Baldur last fight in 2018, Kratos while still holding back can match Baldur , but he can stomp Baldur moment he goes Spartan Rage mode. But note he still isn't quite murderous despite the rage mode.
3) Then comes the part where Kratos is actually willing to kill, and how and why Kratos is willing to kill further determines his power.
Let's look at last example to Kratos vs Baldur. He matched Baldur in base and stomped him in rage mode, but when Kratos decides to kill Baldur he casually snaps his neck in base even though Kratos is sombre, regretful and reluctant.
I am sure we can find different fights where he Kratos was much more willing to kill and performed much better as a result without even rage amping.
4) Now we come to juicy part, a Bloodlusted Kratos. Despite one's expectations there are surprisingly very rare moments we actually see Kratos bloodlusted.
1st example, Kratos&Diemos vs Thanatos, the Death God is dominating the fight despite being tag teamed by the brothers, almost defeats the duo and kills Diemos. Already we see Thanatos is a formidable opponent who is stronger than combined power of the brothers, let alone individually.
But the moment Diemos dies Kratos and goes bloodlusted he almost one shots and detransforms Thanatos back to a humanoid and then takes his sweet time in slowly killing the Primordial.
2nd example, Kratos vs Zeus in last part of 3. Despite entire journey of game requiring Kratos to find the Pandora's Box to defeat Zeus. But box was always and empty and Kratos managed match and defeat Zeus without it's power.
For simple reason that Kratos was bloodlusted. First fight Zeus threatens Pandora and gets almost crippled by Kratos, 2nd fight after Pandora's death Kratos finally managed to kill in a epic battle. All the games and the entire story has lead upto this moment, which shown by how much Kratos is one track mind to kill Zeus, the entire world be damned.
------×------
When I put in perspective everything this way, Thor vs Kratos becomes much more easier for me to analyse, because it revolves around theme of rage and bloodlust but also most importantly being "Calm and Reasonable".
It's Kratos displaying his character growth by trying to prevent Thor by going down his own path of destruction. Their entire theme revolves redemption from making bad decisions in rage, taking a step back and being rational.
Now let's look at both fights.
1st fight Kratos is unwilling to even win let alone kill Thor, so he gets clobbered and almost killed. When Kratos let's tiny bit of rage show he knocks out Thor's tooth.
2nd fight Kratos is trying knock some sense into Thor. Defeats him without needing to kill Thor. This is despite Thor being bloodlusted.
We can see in it's not just rage but also killing intent which matters in determining Kratos' strength.
So I ultimately believe while Thor is definitely near 3Kratos/Zeus in a general sense in power level, he cannot hold a candle when either Kratos or Zeus are bloodlusted. They murder him.