CZ8 series is the commercial version of CZ7, so many parameters are designed the same.
CZ7's rocket body is smaller than Falcon 9, and the first stage mainly relies on boosters to compensate.
One requirement of the CZ7/8 original design was to replace CZ3. So to be compatible with the three-stage rocket design, the second stage is relatively small.
CZ7/8 second stage is relatively small, and the engine thrust is also on the low side, because dual small engines are paired with relatively large tanks. Actual gravity losses are large, and structural losses are also relatively large. So payload capacity is inferior to Falcon 9.
As mentioned many times before, many Chinese rockets consider multiple configurations for one model, especially the compatible design of two-stage and three-stage rockets.
Therefore, the designed two-stage rocket configuration is often not the optimal solution for a specific orbit, but the optimal solution after trade-offs of payload capacity for multiple orbits with combined configurations. While Falcon 9 is the optimal solution for two-stage rocket design, with a design philosophy of forcefully covering multiple orbits.
That is to say, Falcon 9 has the maximum payload capacity in LEO orbit. Actually, considering missions like GTO/LTO orbits, Falcon 9's payload capacity becomes insufficient. It drops very quickly.
Falcon 9, Falcon Heavy, and Starship all have this problem: one common rocket model is used for several different orbits.
China's rockets. From CZ2/3 series to CZ7/8. To CZ9/10, all are compatible designs of two-stage and three-stage rocket configurations, with different rocket configurations for different orbits.
It's just a difference in design philosophy. Several of China's commercial rockets actually also have the idea of two-stage and three-stage compatible design; if you look carefully at the structure of the rockets.