From what I understand from reviews, the only model of this generation to really suffer from significant thermal issues was the 2018 - the 2016 was a little shaky, but the 2017 improved upon it, and as you say the 2019 runs really well all things considered too. By contrast the 2013, 14, 15 retina models are notoriously hot running/ noisy machines when equipped with a dGPU (the Iris only models are much nicer in this regard) the '14 in particular with the 750M GPU had(s) a reputation for maxing the fans/ throttling back and draining the battery while plugged in under heavy load.
Of course the TB models are riddled with by now well known issues, so overall the retina generation will probably be remembered as being significantly more successful but on this metric the TB models actually took a step forward IMO. As you allude to, Intel's 180 from heading towards cooler chips to significantly hotter and more power hungry ones is a big factor in this, I'm not sure how much warning Apple got for the 2018, but I'm pretty sure it would take quite a while to totally redesign a machine and if they were up against the clock, there wasn't really a lot they could do.
It will be interesting to see what direction they take with the next generation machines later this year or next. I'm not sure when the Pro line will move to ARM, but once Apple is fully in control I think thermals and sustained performance will be something Macs excel at.