I upgraded from an S III to an S7 this past June and it has upgraded its operating system to Android 8 or Oreo and I've never had a problem with it overheating and I use an ANKER wireless charger which usually charges the phone in about 2 hours which I do in the evening. My phone is usually still at 50% or more when I put it on the charging plate. I bought it new for $325 from BOOST which uses the Sprint Network. In my opinion it was a steal and by July a new S7 was no longer available...
I grew up having to make my pennies stretch as my father died young and I am one of seven children. It is ingrained in me to make it last and take good care of things.