For a long time I used WAR in Arena. Both WAR and MRD are powerful and fun. I play with a control and I tend to go as MRD now so I can place Enliven over Defiance and Invigorate over Inner Beast on my primary crossbars. To use WAR as effectively, and I would gladly trade the cross skills for WAR ones, I would need to place Enliven and Eagle or Regain Feathers in an accessible place on my hotbars. It would not be impossible, and I plan on experimenting in the future, but for now my muscle memory is set this way, and it is going well.