why take Russia more seriously than North Korea?

I'm reprinting, here, an answer I wrote to a tweeted question I saw over at ROK Drop: "Can someone explain to me why so many knowledgeable people take Putin's thinly-veiled threat to nuke enemies seriously but dismiss Kim Jong Un's naked threat to nuke SK & US? I mean, Ukraine isn't even Putin's core interest, whereas SK surely is to Kim, who has 50+ nukes."

My answer (slightly edited):

I'm just an ignorant foreigner, not a policy wonk, but at a guess, Kim knows that the moment he starts a war, he’s going to lose. Whether he uses his nukes or not, whether China ends up helping him or not (and if China does so, revealing its hand, it almost surely loses South Korea as a trading partner), North Korea will get bulldozed by forces far larger than it. Unlike Russia, North Korea doesn’t have huge oil reserves to use as a bargaining chip, and any long-range strike it might attempt against the US or US territories can probably be met by missile-defense systems. North Korea’s best bargaining chip, right now, is fear of conflict and the ensuing devastation to South Korea (although I’d have faith that South Korea would recover from a conflict far faster than North Korea ever could). So North Korea knows it can only get away with little strikes and incursions against South Korea, or with the tentative-but-provocative firing of its missiles toward Japan.

Russia, by contrast, doesn’t know or acknowledge anything like this. Putin established a “red line” about Ukraine long ago, so his current move, while perhaps surprising in its timing, shouldn’t be shocking. He hasn’t suddenly gone crazy, any more than Kim Jong-eun is crazy.

Russia is, overall, a bigger, more serious danger. North Korea threatens and blusters, but it has never moved to take over anyone else’s territory. And we all know why: it’s too poor. Its equipment is old and outdated; its army is hollow and starving. Any major conflict would last, at most, weeks (perhaps followed by a long occupation/mop-up). That, in my humble opinion, is why people take it less seriously.