>But hackerrank/leetcode don't test for those skills. They test your ability to memorize solutions to trivia questions, typically things you'd never be asked to do in the workplace.

That's not really true. Most of them are variations on a relatively small set of techniques. Dynamic programming, back tracking, tree traversal, sliding window, greedy algorithms, and minimal connected tree will solve 90% of them. And those are all techniques that are occasionally useful.

Sure, some of them will have some esoteric math or algorithm that makes the solution trivial if you know it. Or sometimes there will be some confusing wording. But so long as they're not like that it's a pretty fair test.