I felt the same when I failed a leetcode interview. The reason behind my annoyance was that I had spent considerable amount of time over the past few years improving my skills in the areas I thought mattered (practicing TDD, design patterns,learning FP etc.,) I felt disappointed when none of these mattered compared to an artificial set of challenges setup in an unreal environment.

I can't say for sure that such challenges (array manipulation, backtracking etc.,) are not typical for a software job but I know that they aren't relevant for my line of work. Even if they are, the challenge of solving problems in a live coding session is not the same for all. Different people need different settings to perform or excel.

But now I am committing myself to leetcode and getting better at it, but it has become one among hundred other things I want to get good at. At some point of time, I will feel the burnout. But I sincerely hope the acquired skills are useful in my professional setting.