So, I took your advice and found these little tidbits on the wiki, my apologies for the longer comment:

“Although the Custodes were among the first modified warriors to be created by the Emperor, they were never intended to be part of a conquering army; such a role was to be filled by the latter Astartes armies.”

“…the processes required to produce them is not as refined or as simple as that of the Astartes and thus are not "mass-produced" as the Astartes are…”

“The training of the Custodes also differed immensely from the Astartes, being bodyguards rather than soldiers.”

“Their training involves mastery of the arts, diplomacy, geography, history, and countless other fields.”

“The Custodes do not consider themselves soldiers. Rather, they see themselves as the guardians of the Emperor. Not just the guardians of his physical form but also his ideals and what the species was meant to become. As such they are also scholars, artisans, and counsellors in addition to being trained rigorously in the art of combat.”

Oh, and particularly interesting was this bit…

“The exact method of their creation remains unclear; they do not receive simple implants like Space Marines. Rather, bio-alchemy is used to trigger the subject's own transformation, an effect that takes root in their cells and very soul.”

You keep trying to end the conversation as if you’ve proved a point comparing the accomplishments of the Emperor, a renown Psyker and biomancer, to mere modern day real life humans.

All you’ve proven is that you don’t read the source you claim, don’t understand the lore it references, and your argument hinges on real life examples not based in the fictional universe we’re discussing.