If you think strength is the only requirement for Hokage, then you're just insane. Oro doesn't seem to be all that strong, having such a difficult time even after he has stolen a new body to fight an extremely elderly man with. Having the new body wasn't enough, he had to summon dead hokages to do his fighting for him (which, having human sacrifices for being the conduit, probably supply the chakra, NOT Oro, all he did was stab them with activating Kunai!). A very cheap, and highly forbidden technique, for obvious reasons.

As for Naruto being hokage .. maybe someday far far off, I actually believe he will achieve his goal, but he has tons of growing to do. Shikamaru is actually already ready for the task intellectually, and I stand by that at THIS POINT in the story, he is a better choice. It is quite obvious that the Hokage's main duty is ANYthing but fighting. How many times did we see the 3rd engage in combat? ONCE! The Kage's main duty is diplomacy and administration of the government .. can you see Naruto spending more than 5 minutes on that without going berserk and incinerating the scroll he is supposed to read and sign? The point I am trying to make (based on Oro's GLARING weaknesses in combat), is that Oro was more INTELLECTUALLY fit for Hokage, and would serve Konoha better by doing the work that is required in a more intuitive and effective manner than someone with less intelligence (ie- the 4th, someone who Naruto is constantly compared to). Based on what little we've heard about the 4th, we know that he was vastly powerful, was very passionate about his village and people, and had some very high-level jutsu. But we don't hear anything particular about him being clever or anything beyond somewhat creative. There is obviously MUCH more to being hokage than just being strong. But the POSITION automatically MAKES ONE the strongest (measured by authority and responsibility) of the village.