The playercard argument should not be used at all from anyone (it creates hostility, turn a balance debate into personal issue and as you say even a bad player can solve (or identify) a problem).
Since nearly all units can be countered but all units are not balanced, an argument that there is a counter to something so it does not need balance changes hold little water...
In this example countering 280 mp 30FU emplacement with 2 volks 2 shrecks 2 puppen (1040 mp 180 MU) is not much of argument either because the same proposed counter accomplice very little if it was support with lest say an HMG...
I have no idea what you're comparing. We're talking just about 280 MP, 30 Fuel Bofors... If I was OKW, I can counter it with just 1 leig + attack ground (330 mp) until it's destroyed. I can use my OTHER units to defend that leig, build another leig, or take other parts of the map and put down my own flak HQ. If they try to repair, well the leig rng will generally kill if not wipe engineers repairing it.
Another post mentioned multiple units like cons, at, riflemen being stationed around it... well that's now 2v2. Where's your ally? what are they doing with the REST of the map? And that's just more fodder for indirect fire.