I am constantly thinking about Merry and Pippin in LOTR and how their character arcs are the opposite of Frodo’s. They’re both young and inexperienced at the beginning and they make a lot of mistakes (Pippin especially in Moria), but when they return to the Shire, they’re full-fledged warriors in the service of kings. Theirs is a coming of age story in the same way that The Hobbit is a coming of age story for Bilbo (I know he was already well past his literal coming of age in TH, but I mean this more in the sense of learning about the world and discovering himself).
Merry and Pippin live absolutely glorious lives post-War of the Ring, and the books specify that they always walk around in the armor of Rohan and Gondor (while Frodo and Sam notably wear plainer clothes). Merry and Pippin both lead the fight for the Shire, while Frodo has to beg them both (and Sam) not to kill anyone because he can’t handle any more death.
And when Frodo leaves and Sam is visibly distraught, Merry and Pippin ride back to Buckland and the narration says that “already they were singing as they went.” It’s not that they aren’t sad about Frodo, but they have amazing lives and they can’t help but enjoy them. Frodo’s story is one of destruction and loss, but for Merry and Pippin, the events of LOTR led them to become noble figures, very much in the vain of Arthurian knights. And even though they’ve experienced tragedies of their own, these tragedies strengthen their resolve rather than tearing them apart.
Reading the books, it’s very clear that Merry and Pippin simply can’t understand what Frodo has gone through. I don’t mean this as a point against them personally, it’s just that they will never know the extent of that pain because their own experiences ended up being vastly different from Frodo’s. LOTR is definitely an anti-war story, and none of its protagonists want to be fighting, but Merry and Pippin end up being the ones who gain the most from their part in it all. While Frodo is clearly a tragic figure, Merry and Pippin are the valiant heroes who return from war boasting of their great deeds. Sam is somewhere in between these extremes, being the “everyman” character and the de facto protagonist of the last part of Return of the King.