But you can't make something extremely cheaper then other techs. It's fair to let your opponents to get some counters against it. It doesn't have to completely obliterate it, but like I told you multiple times. By the time the first stuff rolls out it's 7 minutes. (Early game is not about light verhicles but about infantry gameplay)
7 minutes isn't exactly early game any longer. Soviet T3 gives you access to T70, M5 HT, and the SU76. All of these units fall under the definition of light vehicle due to their HP, armor, and role on the battlefield. 7 minutes is the time most light vehicles come out, the Stuart, Puma, and AAHT all come out at around this time.
Ostheer not having light armor is a part of their design. They get access to their T4 as compensation. THe brummbar and panzerwerfer underperforming are problems, but not problems that would be fixed by making T4 come faster. All a faster T4 with no fixes to weak units would do is make Panthers come too early.
Finally, Ostheer T3 already comes at the correct time compared to other medium tiers. Making it come any faster would allow Ostheer to get medium tanks much faster than any other faction can, giving them an unfair advantage. You have counters to light vehicles in your T2. pshreck pgrens, paks, and 222s are all perfectly viable counters to light armor.
The only thing that needs to be looked at is the M5 AAHT in its current iteration. It should either come later, be weaker, or have a set up mechanic.