Lol so BB;
1. Has wounded Shanks, a Yonko.
2. Defeated Ace, the 2nd in Command of the WB pirates.
3. Classified by strength, 1st div commander Marco=Admiral level. 3rd div Commander is Jozu=Mid-High Schichi level. Making 2nd in command about High Shichi level.
4. BB toyed with Ace. That puts him far above that level.
5. Survived Gura Gura punch from WB and tanked Sengoku's Buddha attacks, and Ace's fire spears. Clearly, his durability puts him at an extremely high level by itself.
6. He defeated Thatch, the 4th division commander without a DF.
7. Island level Black hole. Presumably far more destructive power with his Gura Gura.
So clearly Yami Teach is on some next level shit, overrated is a laughable term when discussing BB. Please let's not even discuss how powerful Post-TS BB is with his Gura Gura.