It could be the way the processors are designed and perhaps Android permits some processes to run amok that ramp up heating. My husband ran into issues of processes quietly running rogue in the background, undetected, that caused severe battery drain on his S7 Edge. Other people have experienced that as well.
Yes, my son had a similar issue the other day, very hot phone (Galaxy S6), depleted battery. It turned out to be the BB-8 app he wasn't aware was still running that decided to go berserk, and Android let it. Phone multi-tasking done wrong.