Because they all harmed him... He calls them monsters... I am making sense just fine but Luffy wank is in your way...
They are more important to the story but not in terms of strength.
Just because they belong to future PK crew doesnt mean all of them are stronger than Supernovas...
The young generations of pirates have muscled their way into New World and they will lead the new generation of pirates...
Whim or not, it is 5 Supernovas who battle the 2 Emperors, not 5 Strawhats...
Pirate King crew is irrelevant, some of them will always be mediocre at best.
When Strawhats take over instead of Supernovas, I will believe it. 9 Shadows are the swords of Zoro's Asura.