First I think it's important to note that you won't be competing as much as you think.
In Elyria players are expected to realize that cooperation is important, coupled with the fact that the map is huge (192km x 96km for all servers but OCE) and you will find that gameplay is going to be a very localized thing. So if you want to focus on leatherwork you may be the only person in a good radius working on leatherwork, as you can choose to spark into a family of leatherworkers and fill the demand in the region.
As has been said above, OPCs can in fact train up to a journeyman level. In the immediate area, that's going to be the go to person in that craft. You won't be competing on a kingdom competition scale for best made leather chest piece without some extra effort, but you will certainly be a go to person in your area of operation.