The ratio of 777s to 747s is tied to day of week and the time of year. This has always been the case. During the summer and on peak days, it is heavily 747s (sometimes all 747s). On off peak days/slow travel periods (for that route), it often becomes mainly 777s. This is nothing new.
That said, I have never agreed to fly one in J on this route. If not 747 UD or F, then its definitely over to AA.