Despite being Shogun, Orochi never sought to rule Wano, his intention was always to bring Wano to ruin while enjoying himself in the process. And in that regard, he was immensely successful. Orochi brought the Kozuki name to the point where it was ridiculed and vilified. When you really look at how Wano fell into devastation and had its peoples’ resolve depleted to the point of hopelessness, you come to recognise how systematic Orochi was in deconstructing the aspects of Wano that represented its identity. From the nations honor, to the pride of its people, to the symbolism of the Samurai and to the hope embodied within the Kozuki name. Orochi was the antagonist Wano created. And when he came into power, he desired revenge.
It may not on face value seem accurate but Orochi is quite intelligent. He is more the mastermind for Wano’s downfall than Kaido. Without Orochi’s efforts alongside Higurashi 20 years ago, Oden would have dispatched Kaido. As strong as Luffy’s Gear Five is, I don’t believe he is currently stronger than Oden who was overwhelming a Kaido in his prime. Zoro could barely handle Enma in his fight against King and Oden was casually wielding two blades of that caliber. Also let’s not forget that the reason Oden held off on attacking Orochi and Kaido was not because of Kaido but because Orochi was holding the whole of Wano hostage. Oden held off on attacking Kaido for five years because Orochi made the suggestion that he would stop the kidnappings. Orochi may not have possessed strength but what he did possess was a mind that could manipulate others. Take Orochi out from this situation and Kaido would have been wrecked. The whole nation expected Oden to save them but what they got was a man who reduced himself into a fool who would dance across Wano regularly for money over 5 years (to satisfy Orochi).
Additionally, the main reason Oden and the Akazaya Samurai were so caught off guard when targeting Kaido wasn’t because of Kaido but because Orochi placed a spy within their ranks. Kaido may have been the main obstacle to liberation but it was Orochi who served to slip up Oden and the Akazaya Samurai (because Orochi knew Oden). Orochi even instigated the destruction of Kuri Castle by directing Kaido there when he mentioned Oden possessed a heir. Because of Orochi’s suggestion to Kaido, Toki was forced to send her son and some of the Akazaya Samurai into the future and use her life as a distraction in order to allow Hiyori and Kawamatsu to escape undetected. Potentially, if not for Orochi’s input, Yamato may have even arrived at Kuri Castle before Kaido realised Oden had a son.
Once Kin’emon and Co. got sent to the future, they almost didn’t escape Wano because of Orochi and Kanjuro. If not for Kin’emon’s error, Orochi would have succeeded in stopping the raid on Onigashima. Kin’emon’s interpretation of Yasuie’s message isn’t something anyone could have prepared for. And Onigashima would have exploded as per Orochi’s plans if not for Yamato freezing the bombs and shielding the other bombs from the explosive Big Mom set off when she reached to grab something.
In terms of the power Orochi knew how to wield, he was an expert. He may have been physically weak and useless in the application of his Devil Fruit power but he is the primary reason Wano is in its current state. Oden lost because of Orochi (and Higurashi) which subsequently paved the way for Wano to fall into a consuming darkness for 20 years.