Never really understood the armor on the JP4. It's a 60 range TD with a relatively small target size and it gets 160HP at vet 2 like you mentioned. Why does it need the armor?. The understand the armour you have to reflect on the original design of OKW. their armour was all durable to help offset thier slowed income. If the jp4 was your only vehicle, getting swarmed by t34s could be devistating. Durability to be able to get the 5 levels of vet was a hallmark, even the lights were above average durabilty- T70 and Stuart were 320HP but the Luchs was 400, iirc the Stuka was 320,and the on top of everything else has smoke.
I don't think it's horribly gamebreaking or anything, just find it confusing
OKW didn't have a snare at launch either so the durability on a casemate makes sense in that regard too.