regardless of your own personal requirements for what makes a game part of this series, Final Fantasy XI IS a part of this series, and the idea of collecting loot to get items that you can sell comes from that. also the items you mix to form better items comes from FFXI's crafting system, using 3 or 4 useless items such as leather skins or iron ore to craft a weapon or armour or whatever else.
a lot of FFXII takes ideas from FFXI and applies them to a single player universe. you can't just write FFXI off if the single player games are following in its traditions.