Yeah, but most Legacy server characters have had head starts in many areas
A few group of players dominating the economy will happen regardless if it's a new or legacy server.
You are just talking about XI, but not about XIV, and if we are going to draw comparisons to something then that's XIV v1.x and not XI.
Even if there was some people making hundred of millions thanks to double meld relic weapons, there was a huge market for everyone else with just a gathering class, or a couple of crafting classes, or none of those classes but just a battle class.
I wasn't a reach player, and Now I'm just starting with a bit of gil because I didn't amass any huge amount of gil, just like most of legacy players. At the end of V1.x I made a lot of gil, and spent a lot as well, not thanks to any big scheming that only some privileged people knew, but just like most, by trading with Materia, by mining Ores, by making Swords for Hamlet, by double melding crafted items, by selling excess crystals, and so on.
And you don't need a headstart or anything like that to be able to profit like I did from July 2012 to October when V1.x ended. I came back to 1.x in June after a 6 months hiatus, with 3 battle classes, Mining and Blacksmith at level 50. Way behind all the people with everything capped, that HQd and 3x melded everything. Did I get discouraged and said it's a lost case I won't be able to make any gil and just give up and do Ifrit until I get sick?
Not at all, and with a light playing schedule since I work full-time up to 11 hours some days, just looked into the market to see what where the highly sought after items, either mined or made by blacksmiths, so I started mining Ores required for lv 48-50 gear, for Hamlet stuff and for relic weapons. Meanwhile I also leveled 3 more crafting classes thanks to levequests mostly and got the remaining Jobs to 50.
At the end of V1.x I had made myself great Materia melded gear, I had managed to get enough gil to buy a the weapon required for the Relic quest, which was insanely expensive and basically took all the gil I had made along the way, but it was all worth it.
Now, coming back to ARR, we don't know yet what else will be there for crafters to have their hands in, compared to 1.x there is one less money making way, which was Hamlet, so I hope something is there to replace it. But even so, Materia, base mats, and relic weapons are still there, and will be the main source of income until we find out what other systems have been set in place.
Players alike will level a new craft, a new gathering class, and they will find an established market where to offload their items to, and if that path seems too low, then the spiritbond way will be the faster and it is not the rich and powerful who will establish the prices, it will be the spiritbonder who do, because since there are so many crafters at level 50 already, there's little room for those trying to exploit others since the demand is not down to a small group of players but a to thousands of them.
Economy-wise there are more advantages than disadvantages in a Legacy server, and the Materia system is there for everyone to take advantage of, on one way or another.
Exploits will happen, and some hardcore players or botters will become extremely rich, but it won't at the expense of those silly new players, it will be equally from everyone, as bad as that sounds, but it's actually a good thing since the individual impact will be minimum.