It is true that Wu lost more able officers without replacements, but consider their actual kingdom as a group. Shu had large families of the Liu,Guan, Zhang,Zhuge,Huang, and others. Wu had a few such as the Sun,Ding,Lu,Ling, and a couple others. My point is that Shu had families to replace fallen officers while Wu had a smaller choice of talented officers. Wei had A LOT of families, most of Wei was families. Cao,Sima,Xu,Guo,Xiahou, Zhang, and many more loyal officers.