In contrast, the science is pretty simple: all other things being equal, a building with high thermal mass will maintain the same average temperature as one with low thermal mass.

This statement. Makes me unsure you know what thermal mass is. If all things are the same they will have the same thermal mass.

If you left a 10kg block of steel on the pavement and a 5kg block of steel on the pavement all day which would become cooler to the touch faster once the sun has set? Obviously the 5kg block of steel.