Cao Cao had other losses other than Chibi and Hanzhong. However, Chibi was the one loss in his career that broke his momentum and assured the independence of the Southland (and Liu Bei) for decades. It is arguable if Cao Cao could even have won at Chibi. Supply problems and logistics were major reasons, and his troops were sick and unused to naval warfare, while the southerners thrived on the water and were used to the climate.
Had Cao Cao won at Chibi and subjugated the South, he would only have Ma Teng in Liangzhou, the feeble Liu Zhang and the mystic Zhang Lu in Yizhou to worry about. Furthermore, had Cao Cao won, the Shanyue would be a major concern for Wei and not a nuisance for Wu. Wei was used to fighting the horse barbarians up north, but how would they fare with the Shanyue?
"To the meaningless French idealisms of Liberty, Equality, and Fraternity, we oppose the German realisms of Infantry, Cavalry, and Artillery."
- Prince Bernhard von Bulow, German Chancellor 1900-09 (attrib.)