I don't know man.
The entire game was built around following
around and finally putting an end to him.
came out of the blue after that and is the very definition of "lol here i am i'm the real final boss" trope-wise.
Future arc gives glimpses into what happens after to the setting/characters (which is kinda cool, as it is with any 'sequel' to a JRPG, from Advent Children to FFX-2, to TAY (yeah i said it) to Xillia 2/Symphonia 2) but then invents a new opposition just to give a plot motivation for the added gameplay shenanigans that had virtually no foreshadowing throughout the entire game. Hence, tacked on. Like I said in my rant, it could better have existed as a 3-part OVA.
But we're going off on a tangent :V I'm up for discussing this more over on Tales community.