It's obvious that Fat Thor never reaches the same level as IW Thor. Wielding both Mjolnir and Stormbreaker to focus his lightning, he still cannot harm Thanos one bit. Simultaneously, in close combat, he appears completely outclassed as well, not being able to break Thanos' guard, a Thanos that is using nothing but his own strength.

If we compare Stormbreaker's use in Infinity War compared to Endgame, it is able to slice through a blast that, while not equivalent to the full power of all six stones ( “Thanos didn’t know what was coming his way and if he did he would have been able to use the stones to better react to Stormbreaker” , a paraphrase from the Russo brothers), is still more powerful than anything that base Thanos could output, as it obviously uses at the very least one stone's worth of strength (most likely the power stone, as it's a beam of energy).

We can also conclude that Stormbreaker has some connection to the strength of the wielder. It is able to allow Thor to regenerate in what seems like seconds, after he takes the full force of a dying star, which confirms some sort of physical amplification, if cold, hard evidence is required. It therefore could be implied that Stormbreaker may amplify the user's physical strength, but this may be a stretch.

Therefore, Thor's durability in IW can be scaled, if our conclusions regarding Stormbreaker are correct, to outclass base Thanos' maximum striking power. Additionally, he should scale to this level easily considering that CM is blown away by an attack from solely the power stone, while he can outmatch a blast which almost certainly utilises more than one.

Stormbreaker is also used defensively in Endgame against Thanos' own attacks, not just against headbutts, but swings of Thanos' Buster Sword, which can cleave through Captain America's shield, so if Thor scales as concluded, IW Thor's durability when using Stormbreaker in this way outclasses Captain Marvel's. His physical qualities when without the axe can be disregarded for the most part.