Arched and spherical structures are the strongest, the skull is the same, the load is evenly distributed. In the movie "Fight in Block 99" the hero breaks his head with his feet, in the movie "Driver" it was also spectacular, but hardly.
Man is indeed an interesting creature. His questions are incomprehensible, let alone nature.
As for your answer: yes, a person could smash the head of his own kind. I will use your examples from Game of Thrones. Scientists have calculated that the actor who played Grigor Kligan (the Horus who killed Oberyn Martell) in real life develops strength that would be enough to crush a person's head with his bare hands.
I'm sure not.
In one of the Star Trek films, a genetically enhanced superman broke the skull of an opponent. He did this for a long time, screaming with zeal. In general, it turned out to be difficult even for a super-strong organism.
From the numbers. The human skull is a very strong bone. For a long time I read somewhere that to break a skull, you need to apply more than 2 kN of force. A person will be able to apply a maximum of about 1 kN.
A man is a very fragile creature.
For example, if you try to bite off your finger, the body will stop you, but in fact it is no more difficult than biting off a carrot.
And everything else is the same, Of course, breaking your head is not an easy task, but it is quite doable. Especially if you are a huge Clegane