To be fair I think it is a proof that the person can learn all of the leetcode stuff and therefore they might be clever/disciplined enough to learn new tech as well.

Although I don't find it very relevant. When I was fresh out of university, I was good with algorithms / data structures (neither of which I use much in actual work), therefore able to pass leetcode interviews just fine. Yet it was at the time challenging for me to learn new frameworks and I found all of the tooling I never heard of rather confusing.

Leetcode is mostly small time snippets, that tests how intelligently you can write nested for loops and if statements. That's mostly it.

If you are looking to hire people to write < 50 line snippets, it works fine. Pretty much useless for everything else.

LeetCode is a filter mechanism, not an entire interview system.

The big companies that have LeetCode in their process also have system design, behavioral, resume review, and experience review as part of the process.

I’m sure some bad companies are using LeetCode as the entire interview process, but it’s not how it’s normally used.