It's unfortunate K. Rool got nerfed, but he didn't get hit as hard as say, Chrom. His nerfs were minimal and while his recovery is now a tad less safe, it's not going to kill the character's viability. It's not like K. Rool was a top tier to begin with, but if he drops any, it won't be much because of this. He also got a slight buff, as although now his down throw won't bury for as long at lower percents, it's much easier to get off his laggier, stronger moves at higher percents for easier kill confirms. Not sure if his dtilt was adjusted in the same way, but that doesn't matter too much.
That aside, I don't think there's anything to worry about. Nintendo isn't nerfing characters to the ground just because they're good against inexperienced players. An excerpt from Sakurai's recent Famitsu article on the subject (which you can find
here):
And in the end, K. Rool was only messed with a little bit. Only the things that are a little stupid like how big his Blunderbuss suction hitbox can be or the hitbox on his recovery making it so safe were adjusted, and those options weren't at all crippled. And his down throw was buffed and nerfed in a way, as explained earlier. His super armor wasn't touched, the power of any of his attacks wasn't touched, and people who call foul and think K. Rool's a "dumb noob stomper" will still exist. And that's fine. It's unfortunate he didn't get any pure buffs, but K. Rool's doing fine, and Nintendo's not dishing out any hard nerfs against characters just because they're really good against less experienced players.