The exact title “Mighty God” that Isaiah gives to the promised child is used two chapters later of Jehovah himself, so it is not a lower rank of deity.

Witnesses sometimes hold “Mighty God” apart from “Almighty God,” as if Isaiah 9:6 gives Jesus a lesser divine tier. The same Hebrew phrase, el gibbor, is applied directly to Jehovah in Isaiah 10:21. That makes the phrase a full divine title, not a demotion. This is a checkable point about the words on the page.