@billg7:
no i ment why didnt he gave it to someone from his group someone like vergo+mera mera=around admiral level(and he could have people stronger than vergo) why didnt he use it to strength his pirate crew(he wants to be pirate king after all) and kept it all this time did he really think of luffy as such a threat that he planned ahead in the event he went against him or something else??
Don Flamingo explicitly said that after the war he wanted to talk to Luffy, because of the Mera-Mera No Mi! So it makes sense for a man, as strong and with strong allies, as DD to keep the DF and not use it until the meeting.
–- Update From New Post Merge ---
@DARK_RITUAL:
That I won't agree until proven wrong.. So cobys rank is not Captain cuz it's not canon?
I believe that Coby post-time skip rank is Canon! It not appeared in the manga, but it was made in a OVA that have character designs made by ODA himself, and I don't see Oda showing new information outside and that not being canon in the manga(well he can later change is mind and because it didn't appeared in the manga it isn't a big problem, but a never see Oda making that).