Modern mobile processors are incredibly energy efficient. Tiny bundles of activity, combining application processors, modems, WiFi, Bluetooth, location sensing and GPU technologies into ever decreasing packages of electronics. These electronics require on electrical energy in order to process information and this in turn is dissipated in the form of heat energy. Modern smartphones are getting thinner and processors are getting more powerful and producing more heat at full load. That heat has to go somewhere; something we are seeing more and more of is how a given processor is thermally limited. That is, as the processor speeds rise to a potentially harmful point, the chip starts slowing down to reduce heat output. This is nothing new as mobile processors have been thermally limited for some considerable time, but it is only relatively recently that modern high-performance cores can generate enough heat that cannot easily be dissipated from the chassis.
The source website has decided to test a number of devices to measure how their performance suffers from heating up. Whilst we know the devices and the benchmark application used, we don't know the number of test runs, the exact software builds of the devices in question, the ambient air temperature and many other factors. However, as an illustration of how dramatic System-on-Chip throttle is, it's a useful place to start and I've included the results at the bottom of this article for reference. These results, whilst interesting, do somewhat miss the point. Yes, these seven devices have different System-on-Chips and different performance. But six of these devices are completely different, with different chassis designs, internal components and software. The manufacturers are free to fine tune their devices as they see fit, which means everything from changing the processor behavior when running a benchmark to adjusting the thermal limits and clock speeds of the processor to keep the device skin temperature down. The odd one out here is the Samsung Galaxy Note 4, which was tested with both the Qualcomm Snapdragon 805 processor and the Exynos 5433 processor.
Do these statistics tell us that we should dump our Qualcomm Snapdragon 80x-powered devices and buy an iPhone? No. What they tell us is that the processor inside our mobile device is capable of working much harder than the chassis can keep it cool. Most people subject their devices to bursting demands - we load a website, working the processor hard, then we read and the processor goes to sleep. We scroll down and the processor wakes up for a moment before going back to sleep. High load benchmarks are simply not relevant to the majority of people. We have simply seen a lot of coverage for the higher performance Snapdragon devices because technology journalists like to work our test devices hard in order to find something to criticize; the story is picked up, modified ever so slightly between iteration, and recycled. And so should we worry about overheating mobile processors? The answer is no, but with a caveat: the gamers among us, the people who run benchmarks every few minutes and for those people who have their device constantly working hard on a heavyweight application or another, then yes, mobile processor temperatures will be a concern - but almost certainly secondary to battery life and functionality.