What you're saying is not true RS gold. MMOs use a auction house similar to wow. In WoW, when you get an item or a pile of items from the auction house, every listing is an item/items that are recorded by 1 player and one participant only. Therefore, if you wished to buy 1000 of a material, you have to purchase piles from people that will most likely be a different cost. In RS, if you wished to purchase 1000 of something, you simply put in a bid, and you get said materials whenever you're either the maximum bidder or there is enough excess of said item to be sold to multiple buyers.

A big one not to overlook would be alching. High alching single handedly prevents any product from getting worthless, and before you write a essay how I am wrong, I oblige you to find an item at which the buy-able G.E cost in addition to the cost of 1 character rune is less than the high alch value of said item, and stays that cost for more than 24 hours. If what you're saying were true, all of longbows would be unworthy, but due to high alching, their prices have remained stable for YEARS.

To say most skills are unworthy in runescape is merely a valid statement if you expect there to be no updates to Runescape ever again. For instance, let us say RS adds a new ore which requires 95 mining to gather, and it's 10x more precious than a runite ore. If you just had 85 mining because runite ore and never leveled past it, you'd have to devote a loooong time to get that 95 mining necessity to mine the ore that is new, so long in fact, the prices of buy OSRS gold the fresh ore will have spiked significantly by the time you reach 95 mining. Yes, it is beneficial to train past the grade of gatherables/craftables.