In the first four seasons (the first era of My Little Pony: Friendship is Magic), most of the Mane Six each had about an average of 1.5 absences in one half of a season (13 episodes), depending on the season.
Then, as the second era began with Season 5, they got more absences, with Fluttershy literally being the only one to have as much as five absences in one half of each of Seasons 5 and 6. But now, it's getting even worse still.
What do I mean by this? Well, let's compare between the two most recent seasons of the show:
Last season, Fluttershy was the first of all the main characters to break a record of appearing in the least number of episodes (16) in one season. But THIS season, Twilight got that SAME amount, and that was the most episodes any character has appeared in in Season 7 episodes! I'm not kidding; nopony at all made more than 16 appearances in Season 7, including cameos.
Really, I don't know what is going on with those crazy writers. I sure hope they improve their skills and give more appearances to our favorite pony friends unlike in this season.