There’s also the fact that Sakazuki does parallel Blackbeard. Both represent 2 sides of the same coin one just being a pirate and the other a marine
If we’re under the assumption that Blackbeard falls before Imu and Imu is Luffy’s final fight for better or worse Sakazuki could be the Cracker or kizaru equivalent before Imu
As Blackbeard like Doflamingo and Kaido were main arc fights while Sakazuki Like cracker or Borsalino are still comparable to them but just aren’t the main fight