i think most shepherds go through this phase. mine went through it around 5 months. whether you can get rid of the leash reactivity or just be able to manage it ultimately comes down to his genetics.
i'd take a little bit of both the breeder and trainers advice. you need to put your dogs in situations so he will learn but you need to keep him at a distance where you still have his attention and can still give him commands. once he is lunging and barking then he is over threshold and your commands go on deaf ears. it takes patience and hopefully your dog isnt too nervy and it gets fixed because even a simple walk around the neighborhood with a reactive dog is a chore.