Causality(Cause and Effect) is one of the most defining aspects our universe, manipulating it at all is a major deal, being able to invert is utterly absurd.
If Rama can literally cause an error in Causality to not pierce his heart through sheer willpower, Karna, a character who literally can still exist without a Spirit Origin(Something that defines his existence as a Servant) through that same willpower? Not a goddamned thing from any Sternritter is doing SHIT.
Actually, Surtr only knows one because he's literally just the manifestation of Ymir's Rage in the Nasuverse and nothing more, the Death Rune.
And to know how Primoridal Runes work:
In laymen's terms, they are basically Commands to the World itself, if a spell happens, the World makes damn certain it happens(Reality Distortion is basically Kyoka Suigetsu, you have runes for Flight, Stasis, Healing, etc.)
Whole list here:
Death Rune Flight Rune Healing Rune Reality Distortion Rune Inertion(Stasis?) Rune Wisdom Rune Speed Rune Shield Rune There are a hell of alot more than these but these are just examples.
But for Surtr, he just has the Death Rune and unless you don't have Flesh and Blood, if you get hit by it? You die, plain and simple. And even if you are a Servant, you are basically required immediate attention and is out of action for like a week or you die, plain and simple(like literally can't even do any real heavy movements)
That's just how bullshit it is. Just hope you can fuck with him and make him miss.