IMHO I believe the right approach is to either ask from a standard bucket of questions that require preparation and advertise which ones to candidates, or not ask them at all. Asking "only a few really easy ones" is becoming a red flag to me.
And what are you testing than? Whether someone can memorize things?
Even though I'm not good at memorizing things every second monkey out there is.
Actually, people relying mostly on memorization for "problem solving" aren't very intelligent in my experience.
Especially in software development you don't want people who can mostly only reproduce things once learned by heart!
No two problem instances are exactly the same. It's all about the context! What is the recommended text-book solution in one case could be the most stupid thing you could probably do in another superficially "similar" case. You want people being able to recognize the difference and act accordingly.
(Of course you need some amount of drones in every company. Especially when your company is big. Not everything needs highly skilled and highly intelligent employees. Also there is only a given amount of adequate people available at all. If you're big you can't be too picky if you want to hire enough staff in a reasonable time frame. But those are problems of really large organizations).
But what if too many people pass those filters?
Then we move onto mediums.
But what if too many people solve those?
And that is how we reached the current state of interviews.
Because there is a difference between writing FizzBuzz and solving one of those dynamic programming problems that are so common in competitive programming. For the former, I am surprised you can even work without being able to to this, for the latter, you pretty much need special training that is not very useful in most professional settings.
I never took a leetcode style interview so I don't know what is generally expected. If you are expected to do hard problems, it doesn't test much besides your leetcode skills. But easy problems look like a pretty good filter, assuming the stress of the interview isn't blocking you, which is another problem.