I've had about 500K BIS in the same period and I've seen it many times, both domestic and international, though my larger point for the period 3-5yrs ago (and less so the recent past) is that the option to UFC by buying-up to the HUAUP fare class (or similar) has always been available but not marketed. You just had to call reservations and ask to change your fare class to the lowest F. I did this a grand total of
oncein that period FWIW, so that's the experience I am speaking from, though I know others (not on FT) who had done it more often.
So two things specific to UFC have changed in those 5yrs just on the UA side - it's now marketed, and they waived the up-fare change fee.
Those changes alone are not what we face today, however; that in combination with holding back NF/NC, and with the pricing issues for these UFCs (notably ex-EWR) have painted a pretty bleak picture over the past few months for elites - on that I agree with you.
All that said, if someone wants to pay $359 to upgrade to F for IAH-MEX, meh... I can handle the 763 mile flight in coach.
FWIW, that's the exact amount my girlfriend was offered to upgrade that segment in January of this year from a G fare. We passed, she eventually got the EUA.