I had a good time reading this thread. Forums are such forums.
I have the whole range of Pis from the original B to 3B+ and I can relate to thermal issues of 3B. I had to use it under heavy load with a copper heatsink and a fan to dissipate heat. After that implementation of cooling solution I managed to overclock 3B up to 1350 MHz and got 40 Celsius in idle but less than 80 under 100% load.
3B+ seems to address heat issues. It indeed gets hot in much spreaded manner - USB headers get hot as well. However I got overheating icon several times (with force_turbo on though). So, I just putted a copper heatsink and a fan. Now, as I'm writing this post, CPU load is about 15-20% and temperature is 38 Celsius which is very nice.
3B+ is a good incremental upgrade that address the most headache-inducing issue of 3B. But I still think 3B and 3B+ should have stock heatsinks as Odroid thingy does though.