Well, it would be inconvenient if the prepared concrete parts keep exploding, that is just wasted.
Well, Rupert was actually not trying to see through Exador’s illusion. He just happen to notice it.
That is assuming that demons do study magic extensively and that they share knowledge with each other. If Tizzy is correct that Demons are slothful, then extensive study and experimentation would be something demons is not in the want of doing. Sharing and cooperating is another things that Demons seems to be not much capable of. In such conditions, knowledge and crafts are more in the risk of dying and be forgoten than being upheld and kept. New ideas and innovation is also something that won’t thrive here.
More likely, as Tizzy is oft to say, the Demons steal these ideas.
And by the way. Where do you get all these ideas Maou? Are studying the arcane or something?