Its not a trade its a monopoly because the PZIV has less sight, less range and less mobility. The PZIV can bee kited all day long and there is very little it can do about it.
You're probably doing something wrong if a Jackson is kitting your PZIV.
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I'm also agreeing the Kubel as starting unit is probably an issue for OKW. In a meta where you must occupy strategic houses and cap critical points early on, the kubel can't hold the line, use cover or garrison. You also can't wire strategic covers before getting your first ST.
If you meet enemy forces with your kubel that early (let's say they push you and find your kubel) you end upstuck with a low life kubel you can't anymore use and you are forced to build a 300mp unit to repair it. If your second unit was Volks, your are a bit doomed already.
Imo, ST as a first unit is okay, the problem to me is how the kubel was resilient to small arm fire early game. With the armor value drop, players should not be able anymore to use it to soak damage while they push with the ST.