I agree with most of the things stated in the first post. I would only add that I would like ZD projectiles to be a combo finisher as other projectiles are.
About the shield 4, it is true that to have a limitation on the number of allies that can be affected and on the aoe effect (only allies in front of you) it makes it a bit uneffective, a 360ยบ aoe effect would be nice.
About shield 5, I like it how it is at the moment, even though it is true you will be expose to meles after the push back effect, you can still block projectiles and you can also heal allies and have a combo field. Besides, if you are being surrounded by enemies, you can always dodge away (or simply move) and break the casting, it is not like you are forced to be there for the 4 seconds the skill lasts.