I wouldn't buy an i9 given what I know about Apple and its preference for quietness and thinness over heat solutions and performance. Because if I'm buying an i9, I'm buying it to use it, i.e. push it daily at higher tasks. These are executive computers more than workhorses, let's be honest. The thin and quiet thing isn't why you buy a high powered machine. They're nice to have but if they get in the way, and cost 35%-50% more, then what's the point? I think only a select group of Final Cut users are even going to jump on the i9.So, Apple are running up against a brick wall here..
They want to give users the best performance and best chips they can provide, but at the same time keep it cool.
Most people would get new Mac's anyway every 4 years or so, so Apple probably doesn't see this to be a problem, when your dealing with "a confined space"
I'd like to see test on on these chips but in non-Apple Mac's laptops so see if they experience the same. That'll tell you if its Apple issue in same conditions.