Someone was wrong on the internet, and Samwise Gamgee is the minimum bar readers expect if the character has no change at all. He’s the atypical hero — the hero who made it back home again and could just pick things up where things had been left off. His journey affected him, but it didn’t affect his happily ever after.
He hadn’t changed as a character. He was a good man and a loyal friend before he left and he was a good man and a loyal friend on his return.
Frodo is the hero who can’t go home again. Even if it hasn’t changed at all, he’s changed too much. He’s the war veteran who returns permanently changed by his experiences. Frodo didn’t have to travel to a new world but he had to leave his old world behind. He was the same body, but a different person inside.
Sam never needed to change fundamentally who he was. He adapted to the road by worrying about what he would have worried about back home. Sam, Merry and Pippins return home again, but Merry and Pippins weren’t given the same road to travel or so much to carry. It wasn’t Sam’s burden to carry the ring to the mountain, but he carries it and his friend on his back at the end.
The reason why Sam doesn’t have to change is that the person he was before taking a step on the journey was all the person he needed to be to swing Rosie around when he got back to her. Merry and Pippins didn’t change because they were really asked to. They were treated more as children than travelling companions by their companions, and acted even less responsibly when even a child would know what “no fires” meant.
His story is the opposite of the upper-middle-class kid who works hard and practices lots with excellent instruction until they get accepted into Julliard. Whether Frodo succeeded or the letter starts “We’re pleased–” is outside of both of their control and neither needed to do anything more than to continue to try to accomplish their goal as hard as they could.
But Sam personally or the Fellowship could have failed at any time. The easiest thing any of them could have done was give up. Tolkien establishes that the Shire would be affected last if Sauron wins. Sam could have gone back home and put his head in the sand the longest.
But even that would have been a significant moment of change for him. If the Julliard kid had abandoned their quest to get into the best school in the world, they haven’t even given up on their aspirations yet.
Character development is a necessary part of fiction unless the lack of character change is meaningful. Show the journey of a simple man pitted against the armies of Mordor and show he still can be happy to sit down at the same table every night for almost the rest of his life and that character never needed to change in the first place.
But it’s a pretty high bar.