alt Hacker News> I argue "cleverness" is a learned and honed skill by exposure and exercise.
Even if I were to concede this point, it's certainly not honed by the kind of exercise that OP is advertising. We are deep in Max Howell's "invert a binary tree" territory here.
Doing leetcode absolutely makes your system design better and you don't deploy algorithms you don't know.
Invert a binary tree is kind of a strawman for the absolutist claim that you don't improve the cleverness by practice, but it's an example that not all the practice is useful