Doest matter, you need 5 promotions, not 4. Tried t with a level 4 soothsayer yesterday, didnt trigger (and I had completed the tech tree so my GDR was max level). Had won all the previous competitions, and this was the fifth, at around turn 300.
There are only 4 promotions for the soothsayer, not 5. And I finally did get the achievement. I just had to keep playing "One More Turn" after winning the score victory until the Appease the Gods competition came up again. Then I sacrificed my 4 promotion GDR with my 4 promotion soothsayer and the achievement unlocked.