I think leetcode tends to be a randomized signal because if you've seen the problem before then it's easy, but if it's an unfamiliar problem (or class of problem) then you're basically being asked to be Knuth/Dijkstra/et al., but faster. Algorithm puzzles are fun, but they bear little resemblance to typical tech work.

I think doing very basic, simple things is a better test. I also like asking candidates to explain something that they already understand well. And for code, I like reading it and also getting an explanation about why things were done the way they were. Code reading also seems to be an important skill that is probably more important than writing.