I do not understand why people think a magical shield would have the same defensive capabilities as their unit. Please explain why you expect this. Is the description not good enough or are people just not reading what it does? If I am a Wizard and I create a wall around me, why would that wall have the same properties as I do? Does this magical wall wear the same equipment as me? No. So why would it have the same stats as me?
Edit:
Besides, I literally told you how it works less than 2 weeks ago: