The Bible says that people were sick because they did not discern the Lord's body in the communion meal. That could not be more clear. "For this cause...." It means exactly what it says. So simple. Bringing up other hypothetical situations does not change that and only confuses.
And as I mentioned, all the Israelites in Egypt were apparently made healthy at the first Passover by eating the lamb (Christ's body), and there was not one feeble among them (maybe 2-3 million people or more). That was a miracle.