What? Reflect swords is a no limits fallacy. What it could reflect Gilgamesh's swords? Could it deflect, i don't know some godly universe ending sword? Heck it didn't stop a high caliber bullet at one point. Yeah it has that property but there's a limit to it, it doesn't mean anything that is classified as a sword will just bounce off it, that would be absurd.

That was the first thing, second is, i'm going off stats here, calculated stats. Shirou is literally too fast for Kaynthe's blob to even react (if we are talking full power Shirou or Shirou who has traced something). Shirou is hypersonic, well above mach 5. Blob-chan is supersonic, well below that. That aside though, the easiest case to make for this. Shirou using Nine Live Blade works can kill Berserker. Doing the same to Kayneth would splatter him and his volume across a square mile radius.

People seem to forget this but Shirou tracing stuff is essentially a Servant since he actually matches the stats and skills of the original wielder of the weapon, somewhat at least and that he's one of the few guys who consistently fight Servants with decent results. So yeah, in that regard most Zero Masters are a joke to him.

Next Rin. For one i'd point out that Rin is pretty much one of the strongest "normal" magic users the Nasuverse has. So actually if we're talking about pure magical power, she's above Kayneth. Of course she doesn't have nifty tricks as him, but asserting that she'll just plain lose in a magic battle is a bit far reaching (not saying she'd win either though), HOWEVER all of that stands while excluding the Jeweled Sword. With it the whole match becomes a landslid in Rin's favor.