Originally Posted by mridley2

I recall around 2016-2017 the upgrade rankings were 1 Medallion Status and 2 Fare class Y B M Q K L U…. These two categories were most important. Beyond that was time of request and maybe one other tiebreaker I cannot recall.

so yes not THAT long ago the main factors were fare class and medallion status. In fact I recall overhearing multiple business travelers booking higher class main cabin fares to increase their chances of First class upgrades.