>In my club there is a kid who talks about Sicilian Najdorf and Accelerated Dragon and he couldn't play a simple KP vs K ending.<
That doesn't refute the argument, because some kid you know is bad at endgames :)
>Instead, learn only the basic strategy and ideas of the opening<
Whatever those might be, for the "opening." This is more of the same generally empty advice. It works for 8 year olds, for their first few games where you are trying to stop them from freeing their rooks in the first three moves.

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Reti said that you shouldn't memorize openings, at least when you are a beginner. Instead, learn only the basic strategy and ideas of the opening, because the lines could be wrong and constantly change. I agree with him. Opening theory constantly change, and a line which was "good" even 10 years ago now could be bad. But if you improve your general chess skills, these won't never change. In my club there is a kid who talks about Sicilian Najdorf and Accelerated Dragon and he couldn't play a simple KP vs K ending.