It seems monstrosity requires an organic element. When there isn’t one, monster is more often an adjective than a noun qualifying an incomplete potential for monstrosity.

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Monumentality embodies distant, impersonal forces at work, that pose a terrifying threat because they don’t care about us. Monsters on the other hand, care enough to be deliberately threatening to us.

Includes a recipe for making the perfect monster!
— Reading on contraptions.venkateshrao.com/p/monsters-and-mediocrity