4. Infantry-based AT such as ATGs or Shrecks are its hardest counters. Panthers and StuG Gs end up in the soft counter role since both units combat each other, though they also hardcounter the other two units in the USF Major tier. In a slugfest a StuG G should still win vs the Jackson due to its rate of fire should you close at an odd angle or catch it by surprise. I guess mass mediums could also work depending if the Jackson gets any pricer where it's not cost effective to mass Jacksons against medium tank groups.
Of course the issue is distance, but our main thing will likely be adjust the Jackson's accuracy at this point so it's less viable against medium tanks.
My personal thing is that I want to improve Panther and PIV but the usual scope locks us out. I tried to get the Panther in as a TD/TH to no avail.
Your answer to 4. Is the biggest problem ostheer has right now, especially in team games since Jackson can kite infantry units easily with its mobility. In addition, pgrens are squishy and lose to any infantry once upgraded. They just can't shoot more than once before having to retreat or get wiped, especially with all the rocket artillery and indirect fire flying around.
I understand the changes to panther were left out. It's gonna be a rough patch for ostheer tanks imo.