Choosing one isn't really such a bad idea. You might feel the 30 point loss a little, but it won't be so much that it will prevent you from playing your "lesser" job well. For all practical purposes, it is the same as having to choose whether you want to get gear for your SMN or your SCH. Assuming you are in a FC that does some sort of equitable equipment balancing, it's unlikely you will get the best gear for both. At some point you are going to have to choose what Job of the two you most like, and which you want to excel at.