maybe I'm biased here as a millennial or using it differently than teenagers today, but my feeling is, with "ok" at least you can use it neutrally, even if it's also used for sarcastic eye rolling. At least you can see it in both contexts.
Whereas I haven't ever seen "k" in a neutral context. Seems to me, this one is overwhelmingly used for sarcasm or awkwardness, so I think it carries a stronger message of disapproval than "ok"
...and then there is "kk" which is the exact opposite of "k" and is basically an extra-chill "ok".
I'm absolutely out of the loop as a Gen Xer without kids... but my wife and I text each other "k" a lot. It doesn't have to be an insult. Context above all.
The finest slang of this generation - is it even current anymore? - is "yeet". A word that you can know the meaning of purely from context. We never had anything that rad (heh, heh) back in the 80s.
As a perhaps lazy typing xennial, I use 'k' all the time at work to mean 'ack' or 'yes', context depending. It never occurred to me people could be interpreting differently based on age.
Whereas I haven't ever seen "k" in a neutral context. Seems to me, this one is overwhelmingly used for sarcasm or awkwardness, so I think it carries a stronger message of disapproval than "ok"
...and then there is "kk" which is the exact opposite of "k" and is basically an extra-chill "ok".
Or maybe I'm just imagining things of course...