I’m French and never saw the metal cap but surely it seems perfect for the non aging one. However tradition plays a big role - even if there’s better modern caps.
Regarding the pre modern chemical techniques: not an expert but it seems people used to drink younger wine back then, and used wooden barrels or clay amphora for the older times. For in between times (and the amphora) solid cork as you mentioned seem very plausible.
Considering the material deficit: consider that when you do the microwave cam cooking, the cap double in size and don’t fall down in many small parts. It’s so big it’s basically impossible to put it back inside the bootle. My 2 cents hypothesis is they use glue to use more cork and have a better sealing, enhancing the conservation.
Regarding the pre modern chemical techniques: not an expert but it seems people used to drink younger wine back then, and used wooden barrels or clay amphora for the older times. For in between times (and the amphora) solid cork as you mentioned seem very plausible.
Considering the material deficit: consider that when you do the microwave cam cooking, the cap double in size and don’t fall down in many small parts. It’s so big it’s basically impossible to put it back inside the bootle. My 2 cents hypothesis is they use glue to use more cork and have a better sealing, enhancing the conservation.