I'm not OP. And yes, at first sight that seems to be the main argument. But...

If we're fair to what it is being said, the point seems to be this: churches are like corporations: their goal is to grow in size and revenue.

That is demonstrated by the anecdata of a friend, someone high enough in a particular church, that confirms they only spent 10% of their income on charity.

So the gist seems to be this: if it looks like a duck, swims like a duck, and quacks like duck, it must be taxed like a duck.

Not a bad argument per se. However, it lacks supporting data, preaching for those who already feel that religious institutions are a scam anyway. So, because of that, it's not very persuasive.