The economy will be messed up whether they add gil sinks or not but adding them is the first step to fixing the problem. If you only have 10 million or less now you're pretty much on the poverty line. Any worthwhile gear that is added will be starting at prices of 30 million minimum. I could throw that kind of gil at something and barely notice it gone. So could many people and it's going to cause massive inflation of any rare items once they're added. The only rare items we have now are +3s of end-game gear. Unless you're playing the gil game you'll be out of luck when it comes to the best of the best gear.

People get rich through being mostly sellers. People stay poor through being mostly buyers. It's a player mindset and the only way the distribution of gil will be evened out is if buyers start selling more and sellers start buying more. The buyers probably don't craft much so give them NMs to hunt for drops they can sell to people like me who hate solo NM camping. The rich are getting richer and the poor getting poorer because there's nothing for the rich to buy and the poor are too lazy/have nothing to sell.

Gil sinks will just lower the overall amount of gil on the server, which is good because rich people will reach a point where they have more money going out than coming in while the poor people will have roughly the same going in and out.