The issue is that we think it's gonna be 1 different person for each HK and yet 5 different people for the gorosei.
Like, 14 different people.
1 person can take multiple enemies, maybe at the same time, maybe in different situations.
The Revos can simply stall the HKs, etc.
Plenty of ways this could go,
But, either way,
Luffy, Zoro, Sanji, Law, Sabo, Dragon. That's 6 already.
Yamato could appear again. 7. What if Teach joins the fray? How would his darkness ability interact with the immortality shenanigan?
etc.