If someone has failed 4 first-round case interviews for full-time recruiting and has only passed 1 case interview, does that mean that they suck at casing?

I've seen 3 separate posts about this by now, so I'll bite. 

Honestly without more context, it's hard to say if you didn't pass because of your casing vs. another factor like communication, poor behaviorals, being awkward, etc. If I had to guess though, you most likely suck at casing.

You should have gotten feedback from your interviewers about where you got dinged, if it's consistently the same thing (structure, brainstorming, driving case, etc.), then just work on that. If your feedback feels random/dodgy, it might be one of those other factors and the interviewer just doesn't want to say it outright.

Also, I think LS cases are the easiest type of cases, and when I went through recruiting for LS firms, I literally was doing like the same 1-2 cases each time just with a different disease and different numbers. I feel like that's the one situation where memorizing the process actually helps so doing that would be a way better use of your time than asking this question repeatedly.