I've always thought the solution to over-production is to have some mats be rare. Take the Scorpion Harness in FFXI from 2004. The price of the NQ of that remained stable for years because one of its mats was a claw that had a limited supply from an NM and later a BCNM. This meant you couldn't spam Scorpion Harnesses for HQs in the same way you can a Crab Bow in XIV.
Now what if they did the same with the crab shell component of the crab bow? What if the supply of these crab shells was limited to 2 per day per server? You'd have an NM crab that DoW/Ms could make money off killing, the crab shell would go on the market and crafters would buy it. Since there's only 2 per day and they're likely to stay at a high price, you can't spam hundreds of crab bows until you get a +3. NQs enter the market at a slower rate so their price stays higher for longer too. By the time the NQ market is flooded there is a new bow available that is better than crab bow.
Take the Dodore Doublet, there's a reason they cost 15 million on my server three months after it was implemented. It's because the supply of Dodore Wings is incredibly low, and while that's changing it's because the drop rate is not rare enough to handle multiple linkshells farming it every day. The weapon heads dropped from the goblin and buffalo NMs seem to be rarer and I have never seen any of these weapons for sale. They will enter the market when everyone who wants them in the linkshells farming them has them. Those prices will stay high because the supply is low.
I'm definitely not saying every piece of end-game gear should have a component that can only be obtained via an NM, the crab bow is just one example. The game could have a component only obtained via instances or via a rare drop in a gathering node or multiple sources.
For gathering, let me obtain a superior quality gold ore and break that down into 4 superior quality gold (or electrum) nuggets that can then be used to make end-game items. But have that ore so rare that I'm only likely to obtain about 1 per week. Tough shit if I don't get one in my gathering session, I can buy one someone else got during theirs if I want to synth with it that badly.
It's all about limiting the supply.
The economy will never be fixed for anything currently in the game, that's all trash and it will stay that way. Drop rates and item sources need looking at before the rank cap is increased and I do hope the gold nugget recipe is not going to be 4x gold ore/sand or we'll have the market flooded with gold mats right from the start, unlike darksteel and ebony logs which were removed from the game and will be fresh when the cap is raised. I hope the gold recipe requires an additional mat that can only be obtained from grade 6 nodes. Not because I think every crafter should be a gatherer but to keep the supply down.