I can understand that, but that doesnt translate well to tubs. What you could do for something like that is have ambient room temp at low end of temp scale, then have a basking bulb. To simulate basking in the sun. It still gives a good ability to thermoregulate without needing a direct gradient.
I think his main point is that just because alot od people consider a temperature gradient to be an essential part of their ecology, doesnt mean it is a requirement for them to survive or be healthy, and that animals have adapted to worse conditions than a monotonous temerature within their normal temp range.
To that point i agree, i think they would survive just fine, i just think there would be some level of stress if they have no way to regulate, but even a water bowl big enough to soak would work for thermoregulation even if the air temp was static. There are ways to allow them to thermoregulate even with a static ambient temp was my main point. Soil like substrate with a bark hide so they can burrow a bit, a good sized water dish, a rock, there are just so many options you could add to make an ambient room temp work as a heat that would also let them thermo regulate. As he stated, just look at how they do it in nature when nobody has any control over the temp. It can definitely be done, but i feel it would be better with one of the above options to allow them some way to regulate their own temp, even if the air temp is constant (mine burrow under the water dishes like champions haha)