Whitebeard = 50+ years as a Pirate, ruled over an entire era as King of the seas for over 2 decades.
Bigmom = 50+ years as a Pirate, ruled as an Emperor for decades.
Kaido = At least 38 years as a Pirate, ruled as an Emperor for decades.
Blackbeard = 2 years as a relevant Pirate, gonna fall to Luffy in his 3rd year.
For Blackbeard to surpass these guys as a Pirate, to make his name RELEVANT, he needs to do something absolutely INSANE.