It’s better to look at it as implicit subject derivation rather than some hidden “IT”. What your explanation misses is that the subject derives itself from the topic if it is not explicitly stated. The derived subject from the topic in that sentence would thus be a personal pronoun, not an object pronoun (Not to mention the fact that, in English, using object pronouns when in relation to people is extremely unnatural and rude, a heavy nuance that did not originally exist in the Japanese text and thus, is an improper literal translation.) So the most literal translation would be “As for me, = MacFinch.” which covers the pronoun and post-positional topic particle and then the name and the copula だ. An alternative translation for this that combines both Japanese and English grammar structures is “As for me, I am Macbeth.”
The “As for A” structure is taught in this way to help conceptualize that the topic exists beyond the scope of the subject. When a topic is stated as such in Japanese, it does not have to be restated again and again as subject pronouns like English does which does not have topics in the way that Japanese does, or at least if they do, they are very situational or unnatural and thus nowhere near as versatile. English does not have this kind of topic marker, only subject markers. Thus the translation “I am MacFinch” is considering and prioritizing natural English and taking the derived subject, which is what is stated in the topic, then throwing out the topic as it now only contains redundant information that isn’t necessary to reiterate to keep the English natural.
In essence, the translation of “AはBだ。” to “A is B.” is deriving the subject from the topic and then dropping the topic to keep the English translation natural without losing information or giving it a nuance that didn’t exist in the original Japanese sentence.
This is thrice as long as I was expecting it to be so my takeaway here is that it’s important to understand that some translations exist in the way they do to help conceptualize ideas rather than to be a gold standard for how some sentence structures should be translated, implying that other translations are wrong when in reality they’re serving a different purpose.