User blog comment:TheRealD/Why won't Doflamingo uses his parasite ability on everyone in Dressrosa?/@comment-10543621-20150108061105

If there's anything that really bothers me about the whole 'maybe it's harder to control stronger people' reasoning for why Doffy isn't simply controlling the likes of Luffy, Law and even Fujitora, it's the fact that he managed to control and manipulate Jozu during Marineford war.

Jozu was one of the strongest WB captains, possibly just below Marco, and on top of that, his ability laid in his strength, and yet he was unable to resist Doffy's parasite,

So really, I can't buy the whole more tiring to control stronger people thing. The only thing I can attribute this to would be speed I guess. At the end of the day, to activate his parasite requires his strings to actually hit the enemy. I think so far, when he manages to control people, they're usually taken by surprise. I'm guessing his parasite strings are probably pretty slow and hence he needs the element of surprise to catch his opponents. Luffy's probably been dodging them all while Law's Room will certainly make things more complicated.

To be honest, this is one of the things I'm hoping Oda will provide a sufficient explanation eventually instead of leaving it as a giant plot-hole based reasoning like 'well if he just controlled eveyone, we would't have a story to go on with now would we?' And end up with Doffy powers being as glitchy as onion head and his inconsistent zombies.