[favre49]

You're right, it's true - if you're good at competitive coding you'll be good at LC. But that's incidental. You don't even need to be a Div 1 competitor on (say) Codeforces to be great at LC - the bar is incredibly low. Just being average is more than good enough at interviews. Serious competitive programmers aim to solve problems much harder than Leetcode. Just look at some older ICPC and Codejam problems.

There are some people who basically just do competitive programming to be good for interviews, but they don't get very far - not even to div 1. They reach whatever bar is necessary to clear an interview and quit immediately. The people who seriously compete to go for ICPC World Finals or to get far in CodeJam, they aren't really concerned with interviews.