Well, I will return to my experience as a former mechanical engineer on this post.
There are two different concepts that are being discussed, first is insulation capabilities (heat transfer), and second is heat retention (Specific Heat Capacity). Air is by far a superior insulator to ceramic material, as measured by their thermal conductivities, which are 0.024 for air and between 0.19 and 0.36 for ceramics. Note this is thermal conductivity which is the inverse of insulation, so the lower conductivity number is the superior insulator (air).
Since heat transfer is a function of thickness (and not mass), assuming the air gap in the Weber is the same as the wall thickness of the BGE, then the Weber is by far the superior insulator, almost 10 times better. This is only true, however, as long as the temperature gradient is the same (meaning the inside temperature is maintained as well as the outside temperature).
By contrast, the specific heat capacity is a function of mass, not thickness. While air still has superior heat retention per unit of mass with a 1.012 specific heat vs a 0.90 specific heat for ceramics, the fact that there is an order of magnitude less mass of air than ceramics. The ceramics will perform at much better heat retention once the fire is out, and will be much more stable when their is a change in temperature gradient (like can occur during sporadic wind gusts and changing fire conditions due to uneven airflow.)
So what does this mean? Well, based on my understanding, this would mean that under steady state conditions (constant wind speed, precipitation, outside temp, and fuel burn) I would expect the Weber will offer more efficiencies. Under transient conditions (changing wind speeds, changing precipitation, changing outside temperatures, uneven fuel burn caused by inconsistent airflow), however, the ceramics will offer more stability in internal fire box temperature.
I think this is why you see the recovery rate of the Weber to much quicker than that of the ceramics.
I hope this helps, and if anyone has anything else to add or has a different understanding of heat transfer, please feel free to comment or add.