Lethality =/= raw power. Punches usually have more raw power. Take boundman for example. With basic armament, a Kong Gun catapults Doffy through the city, breaks through Katakuri's superior Haki and sends him through pillars. On the other hand, Zoro pointed out that Pica could stop his attack if his Haki was superior. Sword slashes usually don't have the power to just send an obstacle flying through a long distance. Take for reference the fight between Sanji/Queen and Zoro/King. Sanji catapulted Queen out of Onigashima, Zoro didn't really move King from his place. If you have proper defense, you can block swordslashes comfortably. But if the sword slash is strong enough to breach your defense, it deals heavy damage due to the lethality involved. Zoro has already proven his worth injuring and scarring Zoro even pre power up.