Since I haved used this combination a lot it is not based on paper but on personal experience. JPIV penetrates any allied TD + any stock allied medium tank automatically at any range plus most doctrinal choices too. What do you want in addition? Because of greatest ROF of all Vet0 TDs in this game you should own any stock light or medium tank unit with it and level it until the heavies come out were you will bounce some shots of course.
My experience is based on 2vs2 and up since I play AT with friends usually. We play allied factions more but always play the axis side too (I play 90% OKW then). In 2vs2 and up I have a completely other experience from the one you portraited a moment ago. I'm usually a lot more relaxed in late game with axis. Ask my friends I'm not constantly yelling at them when playing axis XD
Maybe because as axis, you don't care about winning.
But either way, your use of the JP-IV is an outlier, There is no OKW vehicle built less often.
The rest of my points stand.
Axis armour "balanced" on paper. It is not good to use.
I'll take longer range, better rate of fire and higher accuracy and higher damage over time on my allied TD's. (all factors lend to ease of use)
You keep your slower ROF, Slower movement, similar/worse pen, higher cost, higher EHP and higher damage (not DPS, just raw dmg) (factors combined make it clunky to use)