What makes Samwise such a masterfully written character?

>As he stood there, even though the Ring was not on him but hanging by its chain about his neck, he felt himself enlarged, as if he were robed in a huge distorted shadow of himself, and vast and ominous threat halted upon the walls of Mordor...

>Wild fantasies arose in his mind; and he saw Samwise the Strong, Hero of the Age, striding with a flaming sword across the darkened land, and armies flocking to his call as he marched to the overthrow of Barad-dur... He had only to put on the Ring and claim it for his own, and all this could be.

>In that hour of trial it was the love of his master that helped most to hold him firm; but also deep down in him lived still unconquered his plain hobbit-sense: he knew in the core of his heart that he was not large enough to bear such a burden, even if such visions were not a mere cheat to betray him.

>The one small garden of a free gardener was all his need and due, not a garden swollen to a realm; his own hands to use, not the hands of others to command.

Samwise Gamgee is one of the most brilliantly written characters in all of fiction and I'm being completely unironic. The Fellowship sets him up to be a minor character who joins the Fellowship by pure happen chance, and he seems unassuming and feels as though he's a background character with all these powerful and heroic characters beside him (Gandalf, Aragorn, Gimli and Legolas), but by the end of Return of the King he is not only the most heroic and loyal character in the trilogy, but the most integral in the Rings destruction. So much so that the most iconic fantasy trilogy of all time literally ends with him.

>At last the three companions turned away, and never again looking back they rode slowly homewards; and they spoke no word to one another until they came back to the Shire, but each had great comfort in his friends on the long grey road. At last they rode over the downs and took the East Road, and then Merry and Pippin rode on to Buckland; and already they were singing again as they went. But Sam turned to Bywater, and so came back up the Hill, as day was ending
once more. And he went on, and there was yellow light, and fire within; and the evening meal was ready, and he was
expected. And Rose drew him in, and set him in his chair, and put little Elanor upon his lap. He drew a deep breath. ‘Well, I’m back,’ he said.