Arteta telling Xhaka he needed to adapt to play in the laft 8 role supports Dula’s theory Tbf. Xhaka is also quite an unconventional 8 stylistically so again it’s unlikely that’s what Arteta has in mind for the postion.
Agree that Xhaka has it nailed down for now, but once age and form start to take its toll I wouldn’t be surprised if you see something very different in there stylistically.