Despite the Federation having as many as thirty-six generations of standard-type Mecha, they only have twelve generations of core engines. The twelfth-generation engine is the Federation's newest and strongest core engine. Currently, it's only equipped to the exclusive mechs of Ace Mech pilots and a part of the Special Level mech warriors.
When Ji Xinghe previously designed the "Ji" mech with transformation capability, Shen Mu stated that without the twelfth-generation core engine, it would never be truly realized.
The most important part of a mech is the core engine. The weakest part of "Star Moon" was also its core engine, which came from a discarded core engine of an imperial mech. After repairs, its performance parameters were only equivalent to the already obsolete fifth-generation core engine of the Federation.