I haven't played quick play in awhile, and admittedly I suspect my main encounters with Ness were noobs who were trying to pk fire = win against me, and thus didn't have a backup plan when I got in on them, but to me K. Rool vs. Ness feels kind of like a snake vs. mongoose situation, where good Ness vs. good K. Rool give each other a fair amount of trouble. Ness has undoubtedly been able to juggle me and trap me with pk fires, but it never seems to be too long before I can close the space with armored nairs or other armored moves and do the cheesy stuff K. Rool is known for like throwing off stage, then attempting gentleman nairs/fairs knowing that I can still recover. Verdict is still out of K. Rool intercepting Ness' recovery, but Ness still has the same weaknesses regarding that too. Cancel the pk thunder with a projectile, clank, counter, or just eating it (and as you said, K. Rool survives, so if a K. Rool player gets the chance they might as well just sponge the damage to get a free stock off Ness.), and Ness is sucking. It's situational, but given K. Rool has better recovery than most, if a K. Rool player can manage to get Ness into the off stage state where he needs to recover, his versatility, options, and stellar recovery might encourage him to run in and intercept the thunder where other characters wouldn't risk it knowing they couldn't make it back onstage.
Overall, Ness players tend to annoy me, but I've held my own pretty well thanks to proper spacing due to armor, counter reflect usage, sheer survivability, and the fact that K. Rool can be damn oppressive if he gets in on Ness. Ness loves to keep K. Rool away, but being a light character, Ness can't take too many moves from K. Rool before he's losing a stock, and that includes K. Rool infamous down smash that can either eat or bypass another pk fire and smack Ness if he's closed in for a sizeable 18 damage. Now of course I don't recommend starting with dsmash, since it's not going to launch far from 0% and might leave K. Rool open to punishes, but preface it by landing some nairs, fairs, jabs, or ftilts on Ness, and suddenly closing the space and being punished by dsmash seems a lot more scary.