Leetcode tests you on a lot of things, but many of them aren't occupationally relevent. The majority of these people are going to spend their time putting out fires or filling in a paint-by-numbers solution they found on StackOverflow.

You really want your power users to shine? Give them a real (or realistic) problem and let them tackle the problem any way they please. Let them reference the books on their shelf. Let them use Google for help. Truly productive people will flourish in this kind of environment.