I have also made a post about 6800 performance, i am experience same crap. I haven't tried on AC Origins as i don't have it installed.
But on WD Legions, Hitman 2, No Mans Sky, Hitman 3 and Warzone, i am having a worse performance than the one i had on my 1070ti... It's very annoying.
I still haven't found a way to fix it.
But know that you are not alone.
Hopefully is some sort of driver issue for some random unlucky folks that gets fixed... Because if it doesn't I'll never get another AMD GPU...
Fckin 600 euros and worse performance than a 3yr old card...