This is the question of the era. All instructors have a different opinion on the matter and many of them will in fact be correct, or at least provide askers much food for thought. Bottom line, I believe shooters who are professionals or serious enthusiasts are still best served learning to perform on demand with irons first if beginning from zero. Let me unpack the reasoning. First and foremost, there are countless millions upon millions of legacy guns in the United States and around the world that do not have and cannot easily accept an optic of any kind. I believe that a skilled shooter with a generalist foundation should be able to make use of any such gun to good effect despite not having an optic. Second, optics fail, and concerning handguns in particular even the current crop of ultra durable and ultra long battery life MRDS's still have failure rates high enough that make me want to have a backup siding system at the ready. Most of the techniques that people advocate for shooting using an optic after the reticle has failed or gone out flat out suck. Once the fundamentals of shooting are mastered with iron sights, adding a dot or other optic is an exceedingly simple adjustment. The reverse is not exactly equivalent, though the skills learned with a red dot or other optic still translate pretty well. however, I would not necessarily go so far as to say someone is wrong if they begin their shooting career learning on a red dot site and sticking with it for the entirety. These siding systems are ubiquitous and will continue to be the standard going forward for all small arms.