That would be all well and good if the KV8 was useless against vehicles (It can change its gun). Sure it can't take on a panther, but it can easily take out a puma (which is an AT vehicle). It's completely off-topic but your argument is flawed because of it. Also, infantry are a lot easier to kill than a tank.
My argument remains. Obers literally have nothing against tanks. Use anti-infantry vehicles (they are the earliest vehicles). I don't think they are 'OP' at the moment. They might be slightly over-performing but OKW don't have much of a non-doctrinal choice for late game AI apart from them.
You have to remember that anti-infantry vehicles are generally quite fragile. This combined with OKW Volks having schrecks makes it very difficult to kill these units. Obers generally are supported by other Schreck volks, which means approaching them with anti-infantry vehicles difficult.
For Soviets at leat, it is rather difficult due to their tech structure. Getting the halftrack or T70 takes awhile due to the teching costs of T3. These vehicles also have a very small window of opportunity to work their advantage.
So it is true that there are vehicles that counter infantry that come out fairly early, but the design of the factions (schreck volks, fast puma, soviet tiering) make it tough to field a light vehicle in time to push the obersoldatens out