no You are not missing anything ( except bonus AD :D ) it seams that Gateway is not doubling AD during Lliira's event... I can confirm that. Than again, they said "...all AD IN GAME..." :) not through gateway ... :(
Reading all this I'm thinking, is it possible that they are prioritising specific IP addresses (specially when number of players peaks) I'm in Europe, ping is going from bad to unplayable (both PvP and dungeons).. The same thing in STO (other Cryptic Game)