Whether it's correct to call Kim Jong Un deranged depends on whether his actions achieve his goals. He's the top of the pile in North Korea, which isn't a state he created. The craziness that is North Korea isn't his creation. He's doing what's needed to stay on top of that pile, which is sane no matter how much fucked up shit you need to do to maintain that. He'd probably be killed if he let go of total control of power.
Then you have their foreign policy. They're scaring the literal shit out of everyone around them. But think about it, most everyone already despised them and wanted regime change. Post-Iraq, we've seen many pre-existing dictatorships toppled. A nuclear deterrent makes that much less likely. However, it's the "madman strategy". You need to be convincing that you're nuts enough to blow everyone the fuck up or the strategy doesn't work.
In fact, so much of their budget is directed at this one thing, missile and nuclear program, that it shows a single-minded determination and one-track focus, rather than a "deranged" program of military expansion. The idea of a nation with less than 1% of the US's military budget having locally-designed ICBMs is frankly preposterous. The sheer fact that it even seems plausible for them to be achieving this shows how much detailed planning they've done here.