Someone on Twitter mentioned that it's likely due to a lack of vapor chamber cooling. I thought 3nm was supposed to be more efficient...Stainless Steel dissipates heat better than titanium. Maybe that's why there are several threads about heat issues on the 15 pros?
I think the moral of the story is to never be an early adopter. In the past, I've never bought an iPhone within the first month of it coming out. I've always waited until January to see what bugs exist and how Apple deals with them. And I always bought the "S" models, which were minor spec bumps.
I think that's a good policy in general, not just for iPhones. There are always production issues when things first come out. It takes a while to sort those out.