I generally agree with both you and schmeisser when you say that ISI(S) has always been a little further away from AQ central and the typical AQ operation. However I think it's clear that, contra armchair jihadist fantasy, ISIS has dug itself into this pit with consistent overreach. They don't have a monopoly on foreign fighters (Abdul Waheed Majid, the Chechens, etc), and there is genuine jihadi infighting, not the just fake (declared so for ideological clarity) jihadis versus the real jihadis.
Here's another "secondary source" on some of the Chechens with JaN:
http://eaworldview.com/2014/02/syria-qa-chechen-jihadis-jabhat-al-nusra-al-qaeda/