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.
Been really busy with work, but finally got time to write a response.
The problem is when you compare it to other factions, is that at the level im playing at accounting for light vehicles is pretty much mandatory. And while t1 is viable (asiamint showed that enough) more often than not if you go t2, you're getting luchs+puma or just puma, this adds on a lot of more fuel costs than youd be dealing with otherwise. A single puma in practice in terms of timing might as well be an m20+stuart in terms of cost (yes i know its slightly more expensive like 10-20 iirc) but in terms of value the puma is literally only there to fight the two of them, while providing unsubstanial value to the rest of the army. Yet the timing hit you take for that one unit ends up biting you harder than your opponent. This goes even double when you luchs, this is partially a problem with not having a generalist choice. And when you consider those factors, even something like 1 minute difference can have some serious ripple effects.
Basically what im trying to say is this, the cost of your units are required to not only keep you a float, but to push you to an advantage (which you likely wont get) in order to pay off for the timing hits you are going to have to contend with, while your foes will always get the better timing.