Though this has taken an interesting turn, I'm getting back to the original arguments/questions.
I speak from experience, having been building passive solar ICF homes for 15 years in CZ 5 and 6, and living in one for five years.
Certainly, thermal mass is excellent when the diurnal temps go above and below setpoint. We see this for about 4-6 weeks every spring and fall. During this time, most homes are running their heat and night. Our homes do not. That is 2-3 months/year LESS that a well designed home does not require space conditioning. Thermal mass is a key part of this.
In normal climates, where mean daily temperature is not 72 degrees thermal mass would only increase costs. For example, if mean temperature range is 55 degrees, then the only thing the thermal mass did is require your heating system to heat up a huge useless mass And, if the next day it is hot, you now have to spend money on your air conditioning to cool down that thermal mass you just heated up. What a waste of energy!
This is not the case. Thermal mass maintains heat. Think of it this way: you only heat it once for the lifetime of your home, not daily. Perhaps I am missing something, but it seems the argument assumes that one would heat the mass to a point that is above your cooling setpoint. In reality, you heat it to 70 degrees. If the next day happens to be 80, that mass will absorb most of the heat, and PREVENT you from turning on AC. If it stays 80 for days on end, we are still not going to cool the mass to a point below what we heated it to. We only cool to 75 degrees. This means that seasonally, the mass temp only changes 5 degrees up in the late spring, and 5 degrees down in the late fall. never are we cooling a mass we heated, or heating a mass we cooled. Rather, we gain from the mass absorbing/releasing the 5 degrees of stored energy.
Any home, any design, any technology can be used incorrectly, designed improperly, or installed poorly. We don't judge the worth of a system by a badly executed example. We judge it by a well done example. I can barely hit a baseball holding a bat properly; but I am guaranteed to be frustrated if I hold it backward!
The radiant heat situation you described MIGHT happen in a poorly executed home; but this is not at all the case for a well done home. Even at a zero degree design condition, our floors are only a few degrees above setpoint. This just what is required to keep up with the heat loss through the walls, fenestrations, and ceiling. If the sun were to come out and reverse the heat flow through the windows, the walls and ceiling will still be losing heat. The floor would turn off, but it was only 73 degrees at the most. At zero degrees outside, the sun isn't providing more heat than the home is losing (again assuming a well executed home). But let's assume for the sake of your argument that it provides 100% of the heat load of the home at zero degrees. At this point NONE of the 3 degree difference between setpoint and slab temp is needed. Worse case-the home overheats by the 3 degrees of the slab temp. Big deal. The first couple hours the sun stops hitting the windows (around 4:00 here) the home will use up that excess heat, and the floor will kick on again.
So at worst, we were a few degrees warmer than we wanted, but we gained a half day or more of the heat not running!
I think if you lived in such a home for a little bit, your concerns would quickly dispel.