They are looking for positive margins if they're short term switching RuneScape gold, and they are searching for items which can raise appreciably over time if they're long term flippers. Which has nothing to do with whatever point you tried to create in the first location. New content comes out, they could immediately do it because of being maxed out, and they mistreat it to the point where it is not worth their time.
That is pretty much the entire point to playing an MMO. Getting the most from new content and being able to play it when it releases. The very fact you keep bringing up combat as being the best money maker just demonstrates that you agree that gold rushes would be the best way to make money, as the sole time combat is well worth it's if you are geared up and are near max, and do the newest combat related content if it is zulrah, Olm, or ToB. Combat is such a central aspect to any MMO that naturally there will be combat related upgrades than there could be with each skill, that's just a given.
Wrong again. Every top player aside from these fighting leaderboards and stakers farmed till ToB came out Olm of the way. Just because prices drop after a week or 2 does not mean the most recent content is not the best source of income. If what you're saying were true, abyssal demons could continue to be relevant, along with dark beasts, KBD, KQ, metallic dragons, God wars, corp and the list goes on. N0valyfe, who's among if not the most efficient player to play Runescape, was just able to buy RS gold max out so quickly after he had been among the very first individuals to get 85 slayer, and left a fortune off the very first batches of whips to come into game.