Most people who are doing competitive programming aren't good at the harder problems. For example, there are >2500 people listed on the TopCoder Top Ranked Algorithm Competitors page (https://community.topcoder.com/tc?module=AlgoRank), but only the top 115 or so are Red, and only about 415 more are Yellow.

A programming contest, even if you just do the easy problems, can be a more enjoyable way to practice for interviews than reading a book or even going through online puzzles like those on LeetCode.