Agreed. See, my charectors have immortals on their side that they can summon at any time they wish. The only problem is that these are Totemas, and can only be summoned when at full JP (overdrive).
And also, the epiloge happened about 20 years after the Planal Ruin. So yeah, Xion has gone through plenty of shells to get back to where he was, and to be back with some kind of civilized being. Granted, technology advances much faster in some planes as it does in others, but since Xion finally achieved true "Planesmage" status, he was able to mold the single plane into what he felt like he wanted. Time goes much faster in some planes than it does in others, so he went to other planes and helped the other planesmages fix their worlds. This took a while, but in that time of roughly 20 years of age time, he finally headed back to Gran Da Val... "Home" for his wife had enough of fixing the worlds.
And if you are even remotely curious who Xion's wife is...analyze the post where I put Malta in suspended animation. 
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