In which theory does coarcatation aorta with arch hypoplasia fit in? The hemodynamic or the eptopic ductal tissue theory?

Not truly separate. I don't think that these causation theories are completely separate. Coarctation with arch hypoplasia tends to present with symptoms in the early neonatal period, and coarctation without arch hypoplasia may present later in life, but coarcation without arch hypoplasia is commonly seen in the neonatal period, too. Further discussion is beyond the space limitations here.