Why not just make the normal AP and HVAP shells a toggle with different attributes and long change over time? That would promote combined armored pushes against jacksons but still allow it to perform all the roles it needs to in the usf roster, just not at the same time (think isu152)
Or just give usf easy 8's without a doctrine and buff its pen so it can go against panthers. Then we can nerf jakson fire rate and give it more pen so it remains good vs heavies. The easy 8's ai is pretty similar to the panthers ai currently, so I don't see an issue with a pen buff. I would make an extra tier for usf. The extra tier would have e8's, rocket arty, and maybe elite infantry.
The tiger may be a little worse than the pershing at lower vets lvls. However, Tiger doctrines are better than the heavy cav doctrine, lightning war especially. Last time I saw pershing being used in a tournament, I saw ostheer knock it out twice with the tiger and stuka anti tank loiter.