I don't think Thunder Bagua is that impressive. It's just another example of how deadly a character can be with their main weapon. Katakuri almost KO'd Luffy with Mogura, yet his other attacks weren't close to bringing him down. Even Cracker's Pretzel almost cut Luffy's arm off (and it was coated in COA!). As soon as Zoro can cut metal, he one-shots Mr. 1.