I think that the X Division started to take a back seat when Dixie started making herself known.
I'll give Jarrett his due, but it seems to me that it was during the days that he and his dad were calling the shots, that the X Division was seen by most as the high light of most TNA shows.
The heavyweight and tag divisions were good (well all except the fact JJ wore the belt through nearly all of his time in charge), but even guys like Styles were saying that the X Division was the place to be, even after he won the NWA title.