There is much to be said for Sam.
There’s a quietness about him, compared to Dean, that just makes him important. He has a golden soul (when he has a soul lol) and he brightens up a room when he walks in. He has always had dreams and has broken down doors in order to follow them. He knows that those dreams are important, even though they might not have turned out the way he wanted them to.
He knows his brother is important. He knows his brother needs to be taken care of because Dean is too busy trying to watch out for Sammy and everyone else to worry about himself. Sam knows about life. He understands.
And he still doesn’t give up.
This is why he is important.