If we look at SBS 59 in JAPANESE, there was an element that was left out in the English translation (as always).
In this SBS, Oda answers someone who asked him about how he had forgot to draw Garp’s scar in previous occurrences and Oda’s answer is quite interesting, he jokes that it is a special scar which “aches” or “hurts” when “因縁の敵” is nearby.
The VIZ translated 因縁の敵 to “an enemy he hates” (which is wrong)
However, looking at the raw text and translations online we get something very different:
So, from this we get Oda thinks that when a scar aches/hurts, it is a response to a sworn /fateful enemy.
Luffy and Akainu
Oden and Kaido
Shanks and Blackbeard
All of them are sworn enemies, who are tied with scars that are aching.
This confirms that Akainu is Luffy’s biggest enemy, not Blackbeard. Blackbeard has history with Shanks (the term sworn enemies was also used to refer to Shanks’ relationship to Blackbeard in a Databook)
Luffy will beat Blackbeard after he killed Shanks, just like Luffy beat Kaido after he killed Oden. But Akainu will be Luffy’s personal fight.