Whitebeard pirates were already called "the strongest pirate crew in the world" in Oden's vivre card and the members have only gotten stronger. You had people like Vista who can fight Mihawk, not win of course, but Mihawk told him to postpone the fight so he can't take Vista out that easily. Jozu who has the ultimate defense, Marco with his op DF, all of WB allies like Whitey Bay who were WB Commanders during the Roger era, etc.
When you can kill their Emperor and the crew can till be considered a Yonko crew (until BB took the spot which took at least a year) you know the crew was insane. No other crew can maintain that power if you kill their Captain.
