This is true, however it is generally accepted that proto-humans had much higher constitutions as well as greater general resistance to fire, water, etc... due

This is true, however it is generally accepted that proto-humans had much higher constitutions as well as greater general resistance to fire, water, etc... due to their lack of advanced structural dwellings and plate armor. If this is the case, the +1s and +2s would be less necessary and bracelets could, in fact, have been merely decorative. That said, if archaeologists take the time to attune to the bracelets, I'm sure they will discover some magical properties.