I don't think it is possible to improve Leetcoding skills by a huge margin.

I work with hundreds of people to improve their underlying data structures and algorithms skills. Myself and my team have run thousands of interviews at Facebook, Microsoft, etc... and many of us have trained interviewers as well at those companies. Some people get these concepts faster than others but everyone is capable of learning the fundamentals. The bars at these top companies isn't set to gatekeep on Leetcode problems... the problems are supposed to be testing your underlying problem solving abilities and how deeply you understand fundamental concepts. I believe that given enough time, anyone is capable of reaching at least that bar. Some faster than others, and some might get farther than others, but most people are capable of meeting the bar. We work with people who insist on doing hundreds of LC problems and you just don't need to do that many to get to the bar, so you might be spending too much time on harder problems, rather than deeply understanding and internalizing the easy concepts.