Also keep in mind the drag is biased towards one direction. Even though you have a drag set, you typically do not have to fight the drag while retrieving.
If the reel is setup correctly, you will still be able to reel line in easily, And the drag will only engage while line is being pulled out. Different types of reels use different methods to allow the drag mechanism to disengage while reeling in, so you don't have to fight the fish and the drag within a retrieve.
At first this sounds like a pain, but after a little while it actually makes fighting the fish that much more engaging, as you each you and the fish need to pick your moments throughout the fight.
Even though the drag may feel relatively light to pull out by hand, the angle of the rod helps to build additional pressure on the fish
Learning to properly fight a fish on a fly rod, can also make you a better fisherman when fighting a fish using other methods. I'll never forget the day I took my sister fishing, and she hooked her first steelhead on a spinning reel. She still got it, but did just about everything wrong, she never once stopped reeling in throughout the entire fight. (She would probably make a good pro bass fisherman
.) This fish she caught would have never made it to shore if she was fishing with a fly rod.