Well...Maybe not so high.Just compare with a standard T34/85 .
Sure they were more vulnerable,I don´t think the boxy superstructure was armored and seem to be open topped ...Any artillery shell would do the work,even a mortar one.
I like the FlaKPanther very much Why shouldn´t it be like this?It was built in the same workshop as the T34 and maybe at the same time...So surely same materials were used (It is said that the armor came from disabled 251s) and same plans also.
Regarding to the Pz3...Are you sure it is an Ammo carrier ? I have seen the same photo captioned as an early Bergepanzer3. I have even a close up of the cover.When I saw it first many years ago I thought it was some kind of Radar equiped tank!!!