1- The tech timings is more or less related to p4 timing, the light vehicles (puma execpted) aren't very good, and making luchs come a bit later at the cost of being able to choose between a stronger early LV game (with luchs having increased cost+ performance) or an earlier medium is far more interesting than the binary of either going puma,luchs or puma but ultimatetly regardaless of having picked between either choice your medium/heavy (ie p4 or cmd panther) will still arrive extremely late.
I have nowhere indicated that obers need to be nerfed. Rather that volks need to be buffed because obers while decent enough, require a lot of investments to be worthwhile and having more than 1 is more of a detriment than a boon in my experience.
Edit: The soviet change was also an extreme buff, having t70 come out at 7 minutes consistently while retaining a very large part of its firepower makes its an auto pick no matter what and combined with certain doctrines (guards or svt cons) becomes oppressive as all hell.
1- T3 tech timings for OKW are not off by far as well. Iirc, OKW T2 builds need to gain ~10 fuel more than USF and Soviets (UKF is cheaper depending on the side techs chosen) to tech to the "tank tier". T1 builds even out. Therefore, the P4J comes 1-1,5 minutes later than other tanks because it costs 30 fuel more. But as you said it is the best tank, so that should be fine I guess? Unless your point is about its timing, but I don't think this should be sped up without nerfing the unit.
2- My bad, I scrolled to the wrong post while writing this part and was reading Stormjagers suggestion of tying Obers to T3.