It's not LVs that come too early, it's medium tanks that come too late, so LVs have no real counter for extended period of time.
There was a whole series of patches when relic said in the patch notes that they feel LV play is not emphasised enough and so they increased the teching cost of all factions but okw. Then, the okw got redesigned also reciving increased teching cost.
That was when relic screw it up and so the solution should be to reverting these changes. Just lower the price of usf/ost T3, okw flak truck and soviet T4 and it is going to be ok. For ost it would be a good idea to lower the price of BP, not the building.
Except for British, everyone has a universial hard-counter to light vehicles: 1snare+1 AT gun
Medium tanks at minute six are the last thing the game needs