That doesn't seem like the right pair of characters for making the intended point. Here is the context:

Perhaps the most important fact about power is that the powerful are almost always sincere. They honestly believe they are doing good. Every Sauron considers himself a Boromir. And - as Acton observed - every Boromir has an inner Sauron.

Boromir himself was an example of a character who was doing bad but thought (until just before the end) that he was doing good. So, to consider oneself to be a Boromir is to consider oneself to be fooling oneself in just the way that Moldbug describes. Boromir already is just the kind of self-deluded person that Moldbug is saying that powerful people are. It would have made his point better to say that "Every Boromir considers himself a Faramir". Or, "Every Sauron considers himself a Gandalf".