There was something wonky with that formula. I think theymos actually halved those sMerits. I had max activity and I got 200 and I don't know of anyone else who got more than that.
No, was 400 for a Legendary with max activity,
see the following quote as reference. read some posts above someone already posted the theymos's quote.
Is possible that are you remembering wrong or are you 100% sure about it?
So the most you could get is if you were a Legendary who maxed out your activity points in the last year, in which case you would get 1 * 0.4 * 1000 = 400 sMerit.
LoyceV also complained about not getting the max points, so I don't really know if someone got 400 airdropped sMerit at all.