The MG42 gets hard-countered by early units/abilities such as smoke, snipers, almost any kind of indirect fire, or attacks from different angles thanks to its incredibly slow traversal speed. Later on, it's hard-countered by Vet 3 infantry head-on due to their very high DPS, other sources of smoke (REs, for example), and as you said, LVs (or anything bigger).
As for AP countering vehicles; just don't sit in the cone-of-fire. It does a lot of damage, but it's still a low-enough DPS that you can easily react to it.
Also, it's been said many times; if you're having problems with early-game units (like I said, early-game is actually very balanced these days), post a replay.
Smoke does not kill MGs so I wouldn't call that a "hard counter". The only faction that would have an sniper available to it in a timely manner are Soviets.
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