You know what it's something i also felt watching the movies. He was loyal and ready to die for him multiple times. Almost drowned in the first movie, fought a giant ass spider and all the things you mentioned, but i also think that frodo was the ring bearer so like he was constantly being drained, weakened and tortured by the ring. Destroying him internally on the top of the journey so he also did some heavy lifting on his part.

The way i see it without each other they for sure would've died. If it was sam alone he would've been lost in the journey not trusting golem if it was frodo alone he probably would've died due to golem's manipulation. And i liked the Neville comparison but until 8th movie neville wasn't in the picture while Sam was constant.