The title of the thread is mainline city pair cuts..but your narrative suggests you're more interested in downgauges to UX...so not sure if these qualify, but here's a few mainline city pair cuts where there is now no nonstop service at all:

HNL to SAN & SEA (they were Sat only)
LAX-FRA
IAD-PEK (I guess that one hasn't happened yet, but soon)
SFO-NGO
DEN-FLL