Ok, took far too long to reply ... now I have 3 more people to reply to
@qwyxivi
You are right ... but in the end, that is the point.
Sometimes it is better to curbstomp ... sometimes, not always. But the demons are stated to be stuck in the always. Using your analogy, if you have a lot of nukes, it is a good strat to just parade them in a national holiday for everyone to see and get scared ... but you have less than that, but are making them, you definitely do not want to flaunt your nukes until you have enough to ensure a MAD state of affairs, because the guy with lots of them might feel tempted to use some of them to erase your threat wile he can.
@Fushiginiku
Ok, let's resume what we know about demon society. Basically they are designed as a enhaced version of the proverbial hen pecking order: strong demon rules, weak demon obeys. Also, their power level evolves with time and they are not immortal or timeless ( in other words, they begin their existance in a point of time and can die ), so there will be a need for societal arragements when a demon, by gaining experience or knowledge, increases their power more than others. It is hinted that demons do that via fighting. There is also a demon king, that is againg hinted to be so because he is the the strongest of demons.
My point is that, unlike Flamme ( and the author, apparently ) thinks, if you go to nature and see the societal structure of animals that have the kind of societal structure he proposes for demons, the individuals in there do not behave like demons do in here. Powerful ones for sure flaunt their strenght, the rest ... not, to avoid that the powerful ones feel tempted to prove their superiority on them. More, and exactly because of that, younger ones will usually feign weakness in the front of powerful ones to gain time for them getting themselves the skills and stength to do their bid for power, because if a powerful one sense a young one budding into someone that can topple him, he will feel tempted to get rid of him while he can do that easily. Note how diferent that is from the "can't limit their mana bacuse their society depends on it" that Flamme states.
So , I think that either Flamme states explanation is faulty or that there is something else at play that we were not presented to already.
@Red225
Note that Flamme doesn't say that. She compares demon mana show off to human riches show off. In other words, as humans could limit their riches show off, but don't , demons could limit their mana output , but don't. For #reasons.
That said, I kind of agree with you. Demons, unlike it has been said in the manga, do not behave as a natural animal that preys on humans ( in fact , we never actually saw a demon preying on humans and consuming them in the manga, just demons killing humans ). Their society is also too much centered on killing humans to be easily classified as natural and it does not seem to have any support inside besides the potential ability of killing humans. Yeah, if you look it that way, it looks like demons were
designed to
hunt humans ( not preying on humans ) and nothing else.