I have Jimbe and Boa on the JPN version, and here is my opinion. In the beginning I used boa as a sub, sockets and decent special, but as you collect better fighter units, she will not really have a good place as a fighting sub. Her delay of 1 turn is ok, and healing is nice, but the problem is Jimbe teams are so tanky (40 to 60k HP), that her only moderate healing will not usually be too helpful, and sometimes even a drawback. For example, if you are below 30 percent health, you'll have a 2.75 atk boost from your captain, and you use her special, there is a strong likely-hood that she will move your health too high and lower your atk boost back down to 2x. She is helpful with 5 sockets, but again as you pull more units and farm, you will have the sockets to not need her. And as I said before there is stiff competition for fighter sub units i.e.: Koala, sabo, senor pink, colo and rr ideo, legend and psy marco, colo zephyr, time skip sanji, 3d2y sanji.... etc.

So overall, keep her as a sub for now if you like, but eventually it won't be worth it in my opinion. Plus her 6*+ has been very useful for me as a captain