https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10199188/

Found this paper ^ Haven’t read it yet though

I think you may be partly right

But anecdotal evidence isn’t very convincing. I’ve had the opposite experience; found being in Greek and Spanish houses during a heatwave way more tolerable than UK ones, even without AC. Idk about Germany but some older Czech houses feel like ovens when it gets too hot. Lovely for winter though.