I'd like to be able to respond with some good articles or scientific data on the benefits of real ocean live rock, but they are virtually non-existent. I've been able to find some mentions of it here and there and am trying to find more good info as to the "why" because this is a topic that really interests me. I'd like to reply in an intelligent manor and admittedly, not a scientist or even close to one but here goes: I'm not referring to "magic rocks". I'm basing this comment you quoted on my observations working in the aquarium industry professionally with literally hundreds of tanks over the years and my own experiences setting up tanks with both dead dry rock, artificial man made rock, and real ocean live rock. I think we can all agree that a reef tank goes through a stabilization and maturation process, yes? The old guard like Anthony Calfo and others used to say that it look about 1 year before a reef tank had matured. It is my theory that the life contained within live ocean rock including bacteria, sponges, tunicates, detrivores like micro brittle stars, peanut worms, amphipods, copepods, bristle worms, and more help speed up the maturation process and allow for greater margin of error in regards to limiting nutrients and algae growth. The micro and macro fauna contained in live rock, that would "awaken" after a couple to a few weeks would eventually establish a mini ecosystem in the reef tank based on available nutrients. This complex "web of life" I will call it worked behind the scenes consuming detritus and filtering the water.
In a tank that is absent this life, there is reduced competition for available nutrients so things like Dinos and Cyano proliferate in their absence. Depending on the rock and what condition it is in it may have needed to be "cycled" or "cured". With some rock you could start a cycle with the die off on the rock. Other rock was clean and already cured basically ready to go into a tank. This was not a difficult process any more than soaking dead Pukani in bleach or acid is so it doesn't leech nitrate and phosphate into the tank for months. People tried all sorts of things when it came to live rock. Some over thought it and came up with things like "cooking" rock or whatever in effort to kill off whatever perceived evils the rock contained. Hitchhikers could be a pain, that is true. However, with a healthy well maintained system that had good nutrient export, most things like Aiptasia could be kept in check and dealt with with the various tools available. It is my opinion and observation that new hobbyists were more likely to be successful in reef keeping back when real ocean live rock was used as the primary source for biological filtration due to reasons stated above. I'm not trying to say that a tank started with dead rock or artificial rock cannot be successful or eventually lead to a healthy system, just that it makes it more difficult and takes longer to have that mini ecosystem.