Severe GPU throttling freezes 2019 MBP16 after 30 minutes of Civilization VI
I wrote a answer to a similar question; it comes down to the design of the MacBook in relation to the thermal requirements of the CPU and GPU.
So, as to your suspects, I concur that poor thermal design being right there at the top.  As for poor application of thermal paste, it may be a factor, but even the most perfect application of the most efficient thermal paste will only account for a minuscule improvement in heat transfer.
I don't believe it's faulty drivers - could they be more efficient?  Sure, what couldn't?  I also don't believe that you have a faulty GPU, however, the way to confirm that is to benchmark the GPU.  Essentially stress test it to see if it fails.
Could it be a bug in Civ6?  That's likely as well.
As for the reliability of the machine to do the job, I believe you'll be fine for what you bought it for - programming and music.  These machines are very popular for both of those tasks and personal experience with using a Mac in audio recording/production found that even lower end Macs with ample memory and no GPU were up to the task.
I find that MacBook computers (and most laptops for that matter) aren't the appropriate platform for games.  There's a reason most of the gaming rigs you see are desktop builds with ridiculous cooling mechanisms at the forefront.  In fact, I've seen a 2012 iMac (which is essentially a MacBook Pro in a desktop config) outperform a 2015 MacBook pro with essentially the same specs.  The iMac was able to run it's CPU at a higher speed for longer because it remained cooler longer.
Bottom line:  You should be safe with your Mac for work purposes and if you want to game, I'd build a gaming rig.  Besides, it's just pragmatic to keep your recreation off of the device that pays the bills, but that's just my philosophy so YMMV.