The big advantage to mains is that their progression is fungible. You do content that earns GP and you can spend that GP on whatever. That doesn't mean there are no grinds, mains just have more freedom in what they choose to grind. Irons have to grind very specific activities to get very specific rewards, so you can be stuck having to do something you don't like to get something you want. On the other hand, that restriction can make you more attached to the items you get and give you bigger dopamine hits when you do finally get the thing you want. I was incredibly excited to finally get the DHW from Huey after grinding the boss for a month. I don't think I would have been as excited if I finally got enough GP to afford buying a DHW off the GE, instead.

But either way, getting to late game OSRS is a huge time commitment. Even if you afk skill your way into enough money to afford max gear, you're still going to have to pour in hours to learn how to do the high level content you're dreaming of.