Don't you think the D. clan have better things to do, like restoring the Ancient Kingdom for example?
Dragon's role is to overthrow the CDs, once that job is done he can entrust Issho with the rest. This trust was already established when his second in command Sabo had a serious conversation with Issho regarding his ideology, and then reiterated by Oda with another incident in Mariejois, though the details of this interaction are yet to be known.
Dragon's character doesn't fit a FA role, he's a liberator not a governer.