I think there's an element of exaggeration in some of the reports. I routinely monitor the cabin temperature and the only time it ever goes above 25C is at the start of the flight when the aircraft has been baking on the ground. In flight a typical temperature is around 22C. If I see it anywhere above 24C I'll turn the master control down to reduce it to a sensible temperature. The temperature in the cabin is routinely managed by flight crew in this manner.