A persuasive paragraph would focus on how Bilbo was not a hero when he began, but became a hero after the journey.
A theme of The Hobbit is that heroes are made, not born. Bilbo is a hero, but he does not start out that way. Gandalf explains why he did not go and get a ready-made hero.
"That would be no good," said the wizard, "not without a mighty Warrior, even a Hero. I tried to find one; but warriors are busy fighting one another in distant lands, and in this neighbourhood heroes are scarce, or simply not to be found. (ch 1)
Bilbo becomes a hero through his own hero’s journey. He develops bravery and problem solving skills. Although he is just a homebody in the beginning, he soon becomes able to handle almost any challenge thrown at him. He picks the trolls’ pockets, riddles with Gollum, gives the Arkenstone to the Elven King, and helps bring peace among the warriors. You can give specific examples and quotes, and use them as evidence that Bilbo became a hero.