I don't fly domestic very often, but for the past year mine is 100%. I haven't been there since comp upgrades started for companions but in Dec/Jan this year that was also 100% on sponsored upgrades. Again, I'm not the ideal sample but the last time I missed an AA domestic upgrade was January 2020, PIT-ORD.
Will test the system later this month, we have a few domestic flights not attached to our international tickets, but by the looks of it I'm pretty certain we'll clear most if not all of them. Worst case I burn my Amex $250 credit on check-in upgrades.