And while both are the same (lets say you were comparing to identical meals), you have to realize that both need fat added to them-a good shot of olive oil never hurts!
To keep from going rancid, both FD and dehydrated foods are usually near fat free. They are also usally on the lower side of calories, so added fat helps.
As for weight, well, FD can help in weight-but you can lose some taste (if you use commercial prepared meals). I love using FD vegetables, fruit and meats to save weight-as they taste great.
A combo of FD/dried works well when making up meals.