My Dell Venue 8 Pro touchscreen gets hot sometimes, when I'm playing Royal Revolt 2 or FIFA 15 UT for over an hour. And the conditions need to be right too, about 34+ degrees Celsius ambient air temperature with anything above 26% humidity. It gets hot to the point that I'm feeling heat on my fingertips as I touch the screen and I think to myself "if I keep my finger here, it will burn". Luckily enough, the games require me to move my fingers a lot.
My Lumia 930 has never felt that hot on the screen, or anywhere near it. I play Royal Revolt 2 on the phone and it warms up the device. Especially on the back and towards the bottom end. Again, not as hot as I described above. I can hold and grasp the phone with heat discomfort and no risk of burning. When my phone gets that warm, it's a simple enough formula... stop using it and let it cool down! A pretty good indication to get my eyes to focus elsewhere, anyway.
During normal use of the phone, for mission critical stuff, my 930 does not get warm. That is, voice calling, photos and (full HD) videos. Browsing through Internet Explorer for 20+ minutes also does not increase the phone's temperature. I can imagine VoIP calls or Video Calling or 4k video recording might be a bit more taxing... but these are not usual operation for me.
A little common sense, everyone. Every device has the potential to heat up. Some more so than others. Variables are also a factor: ambient air temperature, air density, altitude, humidity, air pollutants ppm concentration, your own body temperature all play a role in the ability to dissipate heat. Then you have the variables that contribute to the generation of heat: activity performed, app used, programming efficiency, length of time. I'm sure there are more.
In the end, This phone is great. This smartphone is awesome. So are all the competitor's devices.
But please, how can you begin to compare how "hot" the device is if you cannot control all those other variables?
Then again, some people will get defective hardware (and it doesn't matter which phone you have) and caution must be taken to ascertain whether you have a legitimate heat problem.