Superman has tactile telekinesis, which means he generates a small, bio-electric forcefield that extends onto anything he touches, an in-universe explanation for his invulnerability, how he can fly seemingly without any noticeable force to push him and how he can pick up large things that don't instantly crush under their own weight.
Naturally, this extends to his clothes, and are thus invulnerable most of the time. To hurt Superman without magic or radiation, you have to hit him hard enough to penetrate through the forcefield and deliver the blunt force onto his exposed body. So heavy hitters like Mongul, Doomsday, Darkseid and the like are able to tear through Superman's forcefield and clothes simultaneously, whereas someone like Batman in power armor might only be able to deliver enough concussive force to inflict physical damage through Supes' shield rather than break through it completely.
But as you say, it really does depend on the artist and writer for each story, as each as his own idea on how to appropriately visualize a brutal fight/a villain's strength.