Comments of chapter undefined of The Legendary Mechanic

I don't get it, why isn't he extracting their genes? It seems author doesn't want to give easy beyond grade A trump card potions to mc. Else i really can't make sense of why he wouldn't make use of this opportunity to milk them a bit. It seems according to author, all beyond grade A trump cards must come from hard to obtain summon cards. Mc can't have easy to obtain potions, because he could have milked hundreds. Especially the pugilist guy, his would be the most useful potions tbh. Mc's only weakness is strength really, and having hundreds of potions for that would completely erase that weakness. But ofc, author doesn't want that, so no potions for mc. Smh...