Some parts of XI were specifically being created with XIV in mind, like Abyssea and the crystals you had to go to are aetherytes and such. Guildleves are FOV mixed with the flexibilty of MMM. These aren't stretches. I think it isn't because FFXI had concepts from XIV tested on them, I think this game failed because their main market was always gonna be those niche gamers and they alienated them.