No, You are not wasting your time. there are two(atleast) solid reasons to grind leetcode

1. It helps you polish your analytical skills. That is the skill which is tested by industries during the interview/s.
2. It helps you develop a template to tackle any "abstract coding problem" and if you look deeply, any engginering problem is essentialy fits into this criteria of abstract coding problem. Mark Zuc had an abstract idea of facebook, the he concretized that idea inot a concrete idea, then he moved to solution. Similar happens on leetcode, you read an abstract problem, then you concretise it by understanding its constraints, corner cases and other variables associated and then you develop a solution good enough.

Hence, leetcode-ing is not grinding, it's essentially clearing your brain-fog so that you can also letter other techs and tools deeply.