To reiterate a couple of the valid points made: No, you absolutely do not *have* to craft. You can level a DoW class exclusively if you wish. I know there are people who have done just that, and I can't imagine they're sitting on much gil, if they've kept up with their gear through the levels. Of course, in the month the game has been out, the economy has changed a lot.
Go back to Sept. 22, *everything*; every weapon, item, material was brand new. Prices were absurd for a rank 7 weapon (remember the 100k + harpoons?) The gil obtained from the rank 1, even the rank 10 battle leves is not huge. Foreseeing this, I started as a fisher, and focused primarily on that, alchemy, and cooking. There was no way I was paying 90k for a rank 7 weapon which I knew would be 10k in 2 weeks. And that's just a weapon, remember there's clothing, accessories, shields, etc. The point is, after the Sept 22 launch, I'd say: No, I don't think it was smart (even inefficient) to level a DoW class exclusively.
Fast forward 3 weeks. The market is now pretty well saturated with low level items (by low level I mean 7-15ish), naturally, prices have adjusted accordingly. Take the 8k you get from a solo level 10 levequest, and now it can buy that rank 7 weapon, of which there are many hundreds floating around. The same goes for lower level clothing (75k for a hempen cowl? .. lol). Players starting the game now, or players who have been patient or not had a ton of time to play, will find it much easier to play just a DoW class.
To speak to the point about repairs for a sec: It would be very convenient to be able to repair all your own gear. By that rationale, a gladiator would be well complemented by armory and blacksmithing. I would say using a NPC to repair anything but your undergarments (and lv1 starting gear) should be out of the question. For any item besides lv1 gear, the fee is quite high, and it only repairs to 75%. The repair materials for most of the gear out there at the moment is cheap and common. I put 5 pieces in my bazaar for repair overnight with somewhere between 2,000 and 5,000 gil as compensation. Ninety percent of the time, by morning, it's all repaired to 100%.
To sum it up, going forward, the ease of leveling a DoW class exclusively will increase. That is to say, materials and services will become more common and cheaper. I hope that gives a clear, and objective answer to your question. All that said, you won't catch me dead without a leveled craft, or two.
I started this character at the CE launch, and played for about 2 months. Haven't touched it since.