None fought anyone serious for the past 20 years.
Kaido and Mom didn't meet for decades,
WB said it's been long time since he even heard of Shanks name.
Shank's last serious battle was daily duels against Mihawk.
Kaido against Oden.
Mihawk been slashing Fodders like Don Kreig for 20 years and meet Vista for the first time
Basically everyone in comfort Zone till Luffy appears and pull the trigger
That's why BB is such a fitting yonkou.
He remained dormant till he found the fruit he was looking for.
And, the moment he got it he has been on the move
-defeated Ace
-with half crew became warlord and then infiltrated ID
- form full crew with level 6 prisoners and entered MF to kill WB and take his Gura
- Defeated Marco and wB commanders to take WB territories
-defeated Wang zhi to take pirate island
- got dfs for his whole crew including a horse lol
And, even after becoming yonkou he is still not sitting idle and is on the move
- invaded RA base
- negged Boa and kidnapped Coby
-Invaded WCI and took Pudding
- and now ambushed Law
He did more than any antagonist we faced so far