I do have a PhD in CS (and even taught algorithms). I solved 500+ leetcode problems during 2 years, and failed a couple of time before finally getting a FAANG position. I'm sure that some people are smarter/faster than others, but in my case, studying was necessary.

Before preparing, I could solve most problems within a few hours. But it's far from enough. You're competing with people who are fresh out from college, solved 1000 problems, possibly who had leetcode classes! Some of my colleagues pretty much know solutions to all leetcode problem, just from the name of the problem.