That seems right. In making a ward against something specific, the ward could work out well enough, as a sort of 'nullifier'. Of course, the ward, as charms and enchantments, would be imperfect; this imperfection would likely be characterized in the ward only protecting against the specific thing it is meant to protect from, having a short duration or only being able to ward off so much of what it was meant to.

Yes, it can be a good defense, but also it has its chinks. :)