Well, you're on it. Arcanist.
Between you and the 'Buncle, you can pretty much solo anything around your level with ease. Not to mention, you've got 3 choices being in Limsa. Arcanist, Maurader, and Rogue after you get level 10 on one of the first two.
That said, keep in mind, you MAY still need to level Maurader to a certain level for support skills for Dark Knight. We don't know how these "Pure Jobs" will operate yet, and MRD has tanking cooldowns. (Yes, Dark Knight is a tank, you may need skills from Gladiator and Maurader if that's what your support classes will be, if any.) So you may not want to opt for the 'fastest' to 15, but the one that will save you the most time in the long run.
Thing is, we're still multiple months away before we may even know that much about Dark Knight. I may be completely wrong. But it is a tank, and you will likely need tanking gear. Any gear you acquire for MRD will likely help your Dark Knight level, so there is that.
That's about all I can offer you for info man. This is a combat game and avoiding combat is going to make the game harder for you to enjoy. I'd probably worry less about wasting your time and more about just having fun and exploring around a while. Take it easy.