Why would thermal mass be a liability? I could see that if there are

Combine large thermal mass with good insulation and you have an ideal
situation. How do I know? My ~800 sq. ft. workshop has a 5"slab and
walls that are 5" of reinforced concrete sandwiched between 2-3/4" of
foam on each side. Gyproc over that on the inside and stucco outside.
The ceiling has R-40 insulation under a white (reflective) steel roof.
In the heat of summer, I open everything up in the early morning until
the outside temperature reaches the inside temperature. I then close
up. I have seen it 27C inside when the afternoon outside temperature
was 42C.

In the late fall I light the pilot on the 25,000 BTU/hr radiant heater.
In the spring, I turn it off. Very economical and very comfortable.

Ted