I don't see any drawbacks on Bifur, yet his threat is 1 lower than it should be.
Splorfindel's drawback implies that he is going to exhaust for questing at least 7 turns throughout the game - which he never will, especially with the Light of Valinor coming in the very same pack.
No good reason? I would disagree with you here. Hobbits live in comfort and safety, they're soft. They wouldn't survive a week of the life Smeagol was leading. He's like Bear Grylls of the LotR universe. He's definetely tougher and stronger than any regular hobbit.