Tom couldn't save the world. They talk about giving the ring to him at the council. He can't leave his lands so the most he could do is to keep it and hide the ring. But tom is literally incapable of being tempted by power, that sounds like it would make him the perfect person to keep the ring but actually it would mean he would just forget about it almost immediately. Giving him the ring would be more dangerous than yeeting it into the ocean which they also discussed and deemed not a good solution because it would only delay things. The ring is magical after all and WANTS to be found, trying to hide it away in those sorts of ways will never work.
Tom is meant to represent untamed nature of middle earth. He isn't meant to be mysterious or even particularly powerful. He is just Tom.