I think you might have misread the graphs. The graph is showing a 4x peak/~6x average improvement in TPS. Because of this the load is less I/O bound and thus CP

I think you might have misread the graphs. The graph is showing a 4x peak/~6x average improvement in TPS. Because of this the load is less I/O bound and thus CPU is able to be fully utilised. If you want to measure efficiency you would instead measure at constant TPS.