Your thinking to hard about it, my original point was just that the StuG III isn't exactly the most durable thing out there
As durable as any other TD with exception of ele, SU-76, JT and jackson.
and the fact at it's counters hit the field before it does (AT guns) means that it won't be OP because the opposing player will have a counter to it.
Same line was used when JT and ele was at its OP prime.
Jackson is still extremely vulnerable to ATGs and people still cry OP for some reason.
"Glass Cannon" typically refers to something that is geared towards putting out a lot of punishment while not being able to take much itself due to various factors such as poor durability or risky nature of use, the Jackson and StuG III are an example of this.
T-70 is glass cannon.
USF, OKW and now sov AA HTs are glass cannons.
KV-2 is glass cannon(compared to other units of its tier).
Pack Howi is glass cannon.
StuG is as durable as any other medium tank and takes exactly the same 4 shots any other medium vehicle does, the only things its not as durable against as any other medium are:
-Pshrecks
-Bazooka
-PTRS
-M-42 AT gun
-SU-76
Where it takes ONE shot less to be destroyed(except PTRS, where its 2 shots).
Against literally any other weapon in game-its as durable as any other medium vehicle.