Let's compare Soviet and OKW tech costs:
Soviet T1 or T2: 50 fuel
Soviet T3 or T4: 120 fuel
Soviet T-70: 70 fuel (need to invest 50 + 120 + 70 = 240 fuel to get out)
Soviet T-34: 110 fuel (need to invest 50 + 120 + 110 = 280 fuel to get out, note: 20 fuel more than double T-34/85s which are a lot better)
On top of that soviets need to tech at leats AT nades for additional 25 fuel. Molotovs are pretty good too, even just for cover denial or winning engagements, another 25 fuel - while OKW comes with schrecks just at the expense of munitions, very cheap grenades and obers have free LMG34s.
OKW T1 or T2: 40 fuel
OKW Flak HQ: 80 fuel
OKW Puma: 100 fuel (need to invest 40 + 100 = 140 fuel to get out)
OKW Luchs: 50 fuel (need to invest 40 + 80 + 50 = 170 fuel to get out)
OKW Panther: 175 fuel (need to invest 40 + 80 + 175 = 295 fuel to get out)
The 66% fuel income doesn't mean anything when the teching costs are dirt cheap. The panther counters the T-34 by miles with just 15 fuel more. This needs to be adjusted. It's even more broken in team games if the OKW player is supplied using the luftwaffe fuel supply (most broken out of these), fuel caches or Opel trucks.
Um... Check your prices for units again...
T34, puma, - (100 fuel, 70 fuel)
Regardless, OKW T1 is a forward healing FHQ, T2 is a forward repair as well as resource conversion (still useful) and T3 is defense that denies planes, infantry, and armor.
As Ostheer and Soviets, for devoting a CE/pioneer to build a tech building, you get... A massive waste of space!
Not luchs, derp