HK were hyped to be Rev's adversary in the manga first thing.
Not to mention, It's clear that those twelve are going to be used as adversaries for the "third tiers" enemies. The strongest (Zoro, Sanji, Sabo and co) are going against the Gorosei + Shamrock and the rest of the mugi against the HK.
That's their role.
Just as the Tobi Roppo did. It's the same for every enemey.
Imu/Kaido--> Luffy
Gorosei/Calamities --> strongest subordinates + allies (Zoro, Sanji, Sabo, etc.)
HK/Tobi Roppo --> other Mugi + Rev's
* Jinbe was only taken by surpruse by Gunko's ability. In the long run, my money would be on him hundred times.