Honestly, I think it's a good thing that Nintendo 3DSes don't get hot/overheat.
Sometimes I find the talk about the Nintendo 3DS being underpowered...well, it just gets on my nerves.
Consider that the Nintendo 3DS was officially announced in 2010 and released in 2011. The contemporary iPhone would be the iPhone 4. The iPhone 4's GPU actually struggles to even attempt just one single shader light in a 3D scene while the 3DS will do it with three without breaking a sweat. They're designed for different philosophies. Back in 2010, a mobile GPU with programmable shader capabilities is basically just...another thing in a bullet list of features when it comes to 3D gaming usage. They're too slow back then for any gaming purposes (in fact, I believe that said shader capabilities back then are actually more for reducing battery usage in UI use).
Same for the system memory. The 3DS might have shipped with only 128 MB of system memory (with 64 MB being usable for standard games; 96 for high-memory), but do also consider that iOS apps back then didn't have too much memory space to use on a per-app basis, the screen resolution for the 3DS being quite low, and the fact that the 3DS has dedicated video memory.
The CPU part is slightly inexcusable, though. ARMv6 is kind of dated when its contemporaries are sporting ARMv7 CPUs. That might have changed with the New 3DSes, but we're not sure about that. I do know that a certain homebrew community said that there are now four cores of the same CPU core type as found in the 3DS, which is a dual-core design, but then an official Nintendo-licenced developer said "wrong" on it, meaning that there is at least one part about the CPU type being incorrect. For all we know they could have swapped out the CPU entirely into a modern design...
I think a lot of this has to do with the 3DS basically having to be "stuck" on a given specification for years due to its nature as a portable gaming console. The specifications might be competitive, or even superior to an iPhone 4 back then on a single-application basis, but in 2015, the specifications, which are stuck in time, pretty much are a joke. The New 3DSes, much less so, though, outside of the display resolution.
Sometimes I think it might be worth it to just go to the SP3 with i3 if I'm thinking of getting the 4/128 model of the S3... On the other hand, though, I don't like fans on tablets.