The issue is not about a gunsmith having the skill to plug a gap without damaging finish or loosening the rib in other areas. The issue is how much rust is there inside where you cannot see it.
In my own case, my preference runs to hammer guns that are now roughly 120 years old and have had a long time to absorb moisture and rust unseen inside. The barrels are not tinned inside and there is nothing to stop rust forming once moisture and oxygen get inside.

cheers Doug