my highest DoW class was 31 for the longest time, yet i have two level 50 crafts and two 30+ crafts. it's definitely possible.

some of the items that goldsmithing/weaving can make sell for a rather large profit margin, especially crafting gear.

for example, crafting gear for levels 15-20 can be HQ'd using mats available from the NPCs, and can sell for 1800-2500 gil each.