Let's go through this list real quick:
Akainu: Fleet Admiral, great portrayal, but no relevant feats to speak of since Marineford. Most likely not the final villain as Imu exists as a being with higher authority.
Mihawk: WSS and Zoro's EOS opponent, has a title no one cares about beyond Zoro, and it goes against the story for him to be the strongest when he will never fight Luffy.
Blackbeard: Recently seen him in action, did not look particularly impressive and still no sign of CoC. Definitely not top 1 currently.
Shanks: Yonko, best haki portrayal, but he is weaker than Mihawk as long as he's a swordsman and he has never been hyped for his individual strength like Kaido (and by extension Joyboy/Luffy), WB or Mihawk.
Dragon: Completely featless, he's carried by his portrayal as the Rev. Army leader and most likely doomed to lose to Imu in the final war.
I would not rank any of these guys at #1 when we have:
Luffy with excellent portrayal as a Yonko and the new Joyboy (only one capable of beating Kaido), and the best set of feats next to Kaido.
And Imu, secret ruler of the world and their one feat thus far being destroying an entire kingdom with seemingly no effort, outclassing literally every other feat we've seen so far.
Do my arguments make sense, or did swordsmen/marine wank scramble everyone's brains?