It's probably the least secure of the ones I mentioned, yes. But even so, it massively increases the search space for a dictionary attack because the attacker doesn't know which algorithm was applied first.

But yes, at the end of the day, the best bet is to just take a mosaic of a random text and place it over the text you're trying to obscure. The reason people use mosaic is because it is more aesthetic than a black box, but there is no reason it has to be a mosaic of the actual text.