Arathorn is the same price as Erestor or an Elven Captain with some wargear. Also with Grey Company(/Dunedain), it's kinda the point to make them entirely bow equipped. That's why they make you take 4 Rangers for every Dunedain to make sure you've got some weak points in your force. The Grey Company is still surprisingly resistant in melee however, particularly with their combat heroes (particularly the newer Strider profile that was released with his bonuses and bow). Never underestimate them, I've played with them in the initial FotR scenarios and the Nazgul are completely outclassed.