There is a learning curve to master any of the features on these machines that goes beyond musicality. Pushing buttons has become a "skillset" in playing modern instruments. Launchpads, sample triggers, fill-ins, etc are all just another group of tools to learn how to use.
With THAT said - Korg "is" a bit more finicky than the rest of the pack. Maybe that's because (IMO) they have more humanized fills than some of the others.
I really think that timing is everything in triggering fills ... on ANY keyboard, but more so with the Korg family. It's like driving a sports car with a sensitive clutch.