Again: It's the Lightning Saga as a whole along with XIV's MASSIVE failure that has really been slowly killing the franchise as of late..
The [FF# has been slowly killing the franchise] has always been said ever since 7 was released. I remember during the years of 7-9 where there would be threads like this, then 10 came out people were doing the same thing.
I never saw anything wrong with the lightning series, i think they did a great job to be honest. 13-2 was fun as hell to play.