You're definitely correct, I've learned a lot while practicing leetcode. Especially about my chosen language (Python). I do feel I'm a better engineer because of it.

I don't think much of what I've learned will be useful in the day-to-day SWE grind. It's really quite interesting, but I cannot recall ever having to remember the skeleton of an iterative DFS before now.

I've taken away more useful lessons from system design studying. If I had my way, I'd spend more timing finishing "Designing Data Intensive Applications" (AWESOME book), instead of figuring out why my oranges aren't rotting correctly or trying to remember how to solve the coin problem using dynamic programming instead of a greedy algo.

On the plus side, once I've got a good memory base and can solve random Mediums and some Hards, I should be OK to pass basically any technical interview - barring random chance. Right now I took a break for xmas and need to go back to it, and that is the hardest part :)