All the types of products you listed perform different tasks. Clay (or a clay alternative) is to remove bonded contaminants where as a product like IronX is to remove chemical contaminants. IronX does not replace clay or visa-versa. IronX is a chemical-based product that eliminates physical contaminates bonded to the surface.
A cleaner wax (also called an all-in-one or AIO) is for light polishing and applying some sort of protection to the paint in one step. The polishing ability of a cleaner wax is very, very mild. An AIO will have more polishing ability than a cleaner wax and can do some minor correction.
An AIO will not (effectively) remove bonded or chemical contaminants. That's a very basic summary of those and I know someone will chime in with more comprehensive and detailed links. For some reason, my search isn't working, so I can't add them myself. Since an AIO has polishing ability it can remove bonded contaminates. However, at the risk of instilling swirls if you don't clay
With your other question, is IronX a must, it's a little more complicated and depends on several factors and those factors can be different depending on the detailer's point of view. In general, I would say chemical decontamination is no where near as important as removing bonded contaminants. That being said, I do take the time (and money, because it is relatively not cheap) to do a chemical decontamination every 12-18 months. If you feel better after decon, then the 12-18 month cycle you have is valuable. What I have found is that if you have a properly maintained vehicle you can pass on the decon step; especially if you don't see much color-change on the vehicle du
