Well, Apple has been producing in China for many years, and most of their products in the past seemed to have better quality control than the 2016 Macbook Pro imho. Flight tickets certainly weren't cheaper back then and those bigwigs probably didn't visit the manufacturing site more often than now for the same reason.
That's why I believe the distance doesn't explain the recent drop in QC. I suspect that a lot of the issues like the clicky keys are actually product design failures that weren't detected during prototyping.
Apple like many western company require China factory reduced the price, and they also seek cheaper replacement for cost saving, for example, Apple use BCM Wifi chip, and the chip will packed with radio module to form Wifi IC:
2015 MB12 use module IC manufactured by Japanese Murata
2016 MB12 by cheap Taiwanese Universal Scientific Industrial with a lot of quality issue.
Also the 2016 MB12 USB-C mux also replaced from America to Taiwanese for cost saving.
Also the Notebook marketing declined and Intel poor sales, Intel make the CPU not stable that before, their CPU but actually their process (14nm) is hard to improved, so they start tweak the chip lower voltage, reduced the safety gap and promote the chip more power efficiency that before but they don't tell you really true is they also reduced the stable and eliminated the "FIVR" used in Haswell and Broadwell back to old system by all voltage changed by motherboard (reliability reduced because motherboard much complex that becobut CPU cost reduced ) for cost save.
Those affect the MacBook reliability become drop.
However, other NB factory like Dell and Lenovo also reduced their quality much more that Apple,
(mean that Apple quality reduce but other reduced just more)
such as the XPS coli whine sound is actually by use the poor or/and reduced components.