Legal? Certainly. A gil is not real-world money. And many real-world companies price the exact same product extremely differently in different countries.

I suppose SE believes that even new characters on legacy worlds benefit from being able to sell things at the 6x and 10x market board prices as compared to other worlds. Unfortunately "most" players don't get most of their gil from those inflated prices. They get it at the same price as on every server, from NPCs and quests. They do spend a lot of it at inflated market board prices, though, so it's extremely regressive.

I hope SE can resolve this by getting prices to reasonable levels in a hurry, but they haven't been able to manage the economies even in 3 months. I don't have high hopes. SE all but admitted being too harsh with gil sinks with the sharp reduction in transportation, repair and other prices already. Their fear of gil had them confiscating it all from early crafters who earned it legitimately at launch, yet bizarrely SE prices the houses so only those type of players can afford it (pre-seizure, of course).