The thing is that the whole "Friendship Reports" plot had been being dropped since season 2: a handful of episodes had no letters for Celestia past season. However, it's also a proof of plot advance, as the mane 6 themselves had been giving the lessons. Of course, some episodes deserved to have Friendship Reports, like Scootaloo on "Sleepless in Ponyville" or the CMC on "One Bad Apple". "Wonderbolt Academy" had RD actually giving the lesson, just like AJ gave it on "The Super Speedy Cider Squeezy 6000" (in fact, the Friendship Report at the end of that episode felt like just trolling)