I think they might beat the revs tbh. Who will all the side characters and SHs fight? There are hundreds of potential allies, and barely enough villains. Some of the HKs or Seraphims will realistically be boss fights taking on multiple named characters.
Some of the Mugis are going against the HK too, yes, but we are talking about Brook, Franky (maybe), etc.
At best Jinbe.
But as you said, there Is a good chance the Seraphims are going to be the ones to face some characters.
That Is the thing though: Shamrock excluded, and partially Gunko because of Imu, when you see HKs you see Morely, Karaus, Brook's etc. Eos opponents. That's the level.
Maaaybe EoS Jinbe for one single HK.