[Marileangorifurnimaluim]

Denethor was defined by his loyalty and his pride, and part of what cracked him was being caught in the crux of the two by the coming of the king.

Aimed at the throne? Not Denethor. Think, he never attempted to rise above his rank. But Gandalf pointed out his pride had swollen to the size of a king's, even if Denethor refused to admit it.

Denethor ruled so long he did not draw a distinction between himself, his role as steward of Gondor and de facto king, and the glory of Gondor. He prized loyalty above all else, which is demostrated is his stubborn attachment to both loyal Boromir and Denethor's clinging to the trappings of steward despite his actual power. Had he been more ambitious and less loyal he would have claimed the kingship for himself. That he refused to do. A noble man. As ruler of Gondor he had both Nobility of rank, and it's pride, and Nobility of spirit, his unswerving loyalty to Gondor. With the coming of the king his loyalty to Gondor would have forced him to give up the former. But he couldn't. He didn't have the humility to step down.

To give over the kingdom would have killed him. He would rather have died the leader of Gondor than crown the King and live out the rest of his life, he felt, in ignomious retirement. In a sense, his end was less tragic than Boromir's, because dying the leader of Gondor is what he would have chosen.

By the way, he did not consider Faramir weak but questioned Faramir's loyalty, primarily to himself which he equated with loyalty to Gondor as a whole. It was Faramir's closeness with Gandalf he resented, not his studious nature which Denethor himself shared. But he had a vindictive ability see the vulnerabilities of others and slam them effectively. That claim of weakness in his younger son, always in his brother's shadow, was a brutal slam but nothing more.