That is of course true.
But strongest does not equal most durable or hardest to kill.
It makes a big difference if you hit an A-class monster with extremely thick skin and the size of a mountain with an nuke, or if nuke explodes in the direct vicinity of a human-sized monster.
After all, you can't be so naive as to say that it won't have any effect on that monster and that it won't cause any harm.
Technically it doesn't. You are looking at it from a physics perspective. It doesn't work that way. Superhuman (level 3 and higher) and Monster bodies are augmented by monster power. It's not the material properties which makes them so tough, it's literally monster magic. And while it's possible to cause some harm, it's insignificant. Nico for example transported so much Lava that it literally boiled a whole lake in an instant and the best that attack managed to do was to get it inside the Asura's eyes, blinding it (probably temporarily) and that thing was already wounded (more wounds = less power = less durability).
Perhaps a certain type of superhuman who is physically weak may be "wounded" by a barrage of nuclear explosions assuming that it's possible to even succesfully attack him, but even that doesn't mean that this is a Lose condition. Ella is physically weak, and she survived a direct Sun blast and completely shrugged off Malik's heat wave which was so powerful that broke reality. All the nuclear arsenal of the world isn't capable of delivering such powerful attacks.
The reasons Superhumans get wounded in the first place is because Monster power is involved in the attacks. For example Ella can summon some spikes to wound Nico which make her seem extremely prone to physical damage. However Nico can survive the vacuum of space. In the latest update MC attacks Eisheth with his strongest
slashing attack, which literally sends her through the floor, and the narrator says that he only managed to break her skin. So it's obvious that our physics model does not work in this case (and this is important because WW tends to stay fairly consistent when describing the various effects). There is absolutely no assumption that can be made other than what is stated as absolute fact in the game or it's an argument made by an authority figure which we can safely assume has tested his assumptions.
So if Xanthe says that human technology is incapable of harming a level 5 superhuman, even one with the worst possible ability, and that his monster-based weaponry does not work on A Class and higher, then that's that. (A Class monsters are insects compared to level 5 Superhumans).
