At least, Simon's skin
is tougher than Thor's. But that's about it. Thor is overall more durable, harder to put down, and has a greater ability to damage-soak. But Wonder Man's skin is nigh-invulnerable. Thor's "flesh" isn't notably dense by superhuman standards & he often repels attacks that might otherwise rend his skin by deflecting them with his ostensibly indestructible hammer.
Thor is also capable of "moving like the lightning he casts" when he really needs to.
Other than skin density, Simon is surpassed in every way...
First Knight, Church of Hulk
that there are several portrayals where he severely struggles against quick/agile opponents. e.g. Captain America, Cobra, Mongoose, Spiderman (although this was Masterson Thor), Gladiator (also Masterson).
So, it is unclear which portrayals are the 'correct' ones.