No, Actually iPhone 4S heats up to 69 Degree Celcius when i still has 4s on 2011 when personal hotspot is on.
I also have 5 back in 2012 it heats to 54 degree celcius when playing games
On my iPhone 5S it heats up to 50 degree celcius not that different to 5 unlike on 4S to 5 (about 15 degrees differences)
On the 6 the highest temperature is around 42 degree celcius on heavy use.
As phone is newer, it is less hotter because cpu size get smaller like NM or something like that. You do know that computer before is about 2 Meters tall that over heats up to 150 Degree celcius ?