Lets look at the parka first. The better parkas are breathable, lightweight and roll up into a small bundle for easy storage. The main function is rain protection from showers etc; it's not a wading jacket.
Now the wading jacket, this is a specialised jacket specifically designed for fly fishing/wading. Firstly it should be made of a quality breathable material similar to your waders it also should have a waterproof zipper and a weather flap to keep you dry, plenty of large pockets and a full large size pocket at the back to store spare reels and your lunch. Velcro cuff straps stops the water from running down your arm while casting. Be sure that the lining of your jacket is made from a non wicking mesh so it does'nt wick water while you are wading. A large hood that is detachable. If you wear a broad brim hat you tend to not use the hood and then it fills with water, if it's detachable problem solved.
