Yes I understand new players who want to try all three new jobs will be in for a rude awakening since they have a huge wall in about 100-150 hours worth of contents to go through. For most normal casual player, it will take a good two weeks before they can reach Ishgard, or longer for others. In any case, think of it this way, you get your money's worth. Take your time, enjoy the beautiful game. Try to mix up your daily activities between dungeons, main story quests, side quests, crafting, gathering, levequest, leveling other classes, etc...

In a way it is good to have one tank job already leveled when you unlock Dark Knight, you will have all your gears at the ready - and you know what to do with the dungeons encounter and bosses. No need to rush, just have fun and make new friends in the game.