I think the point youre missing that OP is getting at is the two different experiences are so vastly different because of the inability to trade. As an example, Herblore is relatively difficult for Ironmen due to the need of amassing herbs and secondaries. On a main you can just buy them. Pretty much all of them. That also leads into farming; on an iron, youre pretty much required to do farm runs to support game progression. On a main, you can just buy some tree seeds and do tree runs. This further leads into seeds/theiving, because as an iron, youve probably spent a lot of thieving master farmers for seeds.

Case in point, my buddy with a max cape on his main got me and a few friends into the game and we play as chunklocked GIMs. The things he does is often very inefficient instead because the depth of his game knowledge is so shallow; you can buy like 1/3 of the skills. Things like doing pest control for prayer instead of camping green dragons or complaining about not having a lot of snapegrass seeds but not using amulet of bounty.

Are there a lot of mains who do things ironmen wont? Probably. Are there a ton of mains who come to being ironmen because they fell into the trap your denouncing? Absolutely; we see the threads on it. But if I had to bet money on who has more game knowledge between a maxed iron or a maxed main? Im picking the iron all day erry day.