Ok, exactly. Rin's normally just physically fit, but normal, the only remaining option is performance thanks to magic circuits. No, there's no mention of Shirou reinforcing himself. The mere presence of the circuits being turned on does this. Projection actually changes Shirou's performance considerably. Letting the sword guide his strikes lets him do things he himself can't, such as stand up to Kuzuki as long as his swords are maintained, produce an A-rank attack(cut off Herc's arm), easily handle Herc's attacks as long as he was focused on projecting rather than being in the fight. Shirou's performance in CQB was outright better than Gilgamesh's, so it's kind of a given that was a superhuman action.
As for Archer, you're literally arguing that a character < 1/10 of his usual ability thanks to mana starving, and getting stabbed by a legendary weapon is indicative of servants as a whole. If all his abilities were degraded equally, his endurance would have a numerical value of less than 3. Not to mention that magic circuits are always producing magical energy unless the user turns them off. This means that the circuit was still active, but he had not reserves, not that it wasn't amping him.
As for Salter, already addressed that, but to elaborate, she was barely conscious, with a deeply wounded body, magical energy can't exist within a body that's too wounded to use it (Caster), and absolutely is not an indicate of her normal durability, and was probably in the state where she's inferior to Shirou and Rin in physicality. Again, outside of that circumstance, the dagger shatters. Also, Shirou's superhuman, especially with Archer's arm.