I think that iron being a micro nutrient, is a debatable topic.
It isn't debatable. The macro nutrients are nitrogen, phosphorous and potassium. All of the others, including iron, are needed in far smaller concentrations, so they are all considered to be micronutrients. No question, using more iron than is in most trace mixes can be helpful to the plants, but "more" means perhaps twice as much, which is still small compared to NPK.