I think the point is that competent developers can solve the problem on the go. You don't have to study for it.
I don't know, maybe some places do have ridiculously hard problems that you just have to memorize the algorithm for, but personally I haven't seen that. It's more like advent of code style stuff that you kind of just figure out by yourself.
Last time I did the gauntlet at Google I was able to solve all the problems.
However I wasn't as fast as others as I didn't recognize any of the questions and had to work through them. Interviewers expect you to be fast, or at least compare you to people who seem faster. Doesn't matter who studied or not, or who will actually perform better on non-leetcode tasks.
Also having kids is a real issue, it absolutely crushes the amount of time you have to anything besides working.
You don't need to memorize the algorithm for, but if you haven't been exposed to those types of problems you will solve them much more slowly. Younger developers are more likely to have experience with more CS style problems than an older LOB developer who focuses more on writing clean testable code. I don't have an axe to grind in this as I am the younger developer in this situation.
I don't know, maybe some places do have ridiculously hard problems that you just have to memorize the algorithm for, but personally I haven't seen that. It's more like advent of code style stuff that you kind of just figure out by yourself.