Irrespective of whether it is a barrier to entry or not (if you define the "market" as "selling any good on the market board" then I guess you could define it as a very low barrier), I still don't think that's a good thing. Any barrier to entry, however you define it, is designed to stop new entrants. Whilst the people who have already levelled a specific craft might benefit from that (low competition therefore an ability to dictate prices) that's not very fair on others. Imagine in an extreme example, 1 player had cornered the Culinary market entirely and the cheapest item of food was 1 million Gil. Is that really enjoyable? In the current market it can't happen because substitutes are available from NPCs at a fixed low price ( albeit they might be inferior ) and there is a low / zero barrier to entering production (you can level culinary yourself) which feels fairer to me.