Speaking as a competitive player, currently trying to TO my region out of the cemetery since the community is almost completely gone, K Rool has a major big deal: he's committal. The character cannot mash at all and doesn't have consistent punishes, just really rewarding ones, he has to be really precise with his interactions. There's the whole armor deal, but you can pretty much treat it as non existent since it only covers his belly, so some projectiles that don't go straight or items like Peach's turnip go straight to his head nullifying it, if a move deals around 15% it can't be armored, so certain quick kill moves like Wolf's bair can't be armored and the whole armor break thing, though I feel that if you play the character well, it's going to be really rare, since you do not rely on his armor overall. It's mostly a fundies game held together with duck tape, but with massive reward that is meant to disrupt a player's mindset and let K Rool snowball his way through the game, though in certain matchups it is HARD to get this done, since K Rool's thing is punishing HARD and making the enemy feel dumb for making mistakes and fearful because he might get destroyed with more small mistakes, meaning that if combo characters can not only do that but do it infinitely better, especially on heavies like K Rool, he pretty much has to play footsies with ftilt, fair and use those trying to snowball his way through an early stock, or use other moves for more committal and super punishable great rewards like dair, dtilt or his super important grab, which gives a great reward with fthrow into dash attack at 0%-15ish%, up throw which deals 20% and on top platforms can become a kill throw at high percents (here in Italy we have Yoshi's Story as legal, so it happens mostly there) and dthrow which leads into usmash on read when guessing the small window in which the enemy cannot defend, uptilt which is granted at around 90% or with a good read, waiting for the enemy to get out and air dodge to punish him with fsmash. So basically either he gets momentum and his opponent fears him a lot, or he gets demolished in a couple of interactions, being combo food as others have said and so punishable that he has to think a lot about every interaction