It is, plus one endgame book.
Even if it's Dvoretsky's Endgame Manual it isn't enough. Theoretical endgames (and strategic endgames too) are so rich and varied that to truly have a firm grasp of them one needs specialized books, such as Secrets of Pawn Endings or better yet, the ECE volumes.
How are you able to say it isn't enough to get me to expert, even though that's basically all I did? It wasn't that hard to get to where I am.
"Easy" approach:
Play 5 to 10 non-bullet games every day. After the game look up the opening. Then looking at the whole game find what you'd consider to be your biggest mistake. Then put the game in an engine and look at some tactical mistakes. This post game work can take 5 minutes (or less) once you get used to it. (If the games are on the longer end of "standard" length, i.e. taking over an hour to complete, no need to be playing 5 to 10, I'm writing this with blitz in mind).
Every other day memorize some openings and solve some tactic puzzles.
Every now and then read a book. One book ever 1-2 years should be fine.
After 10 years of this you'll be pretty good.
Which is mostly to say I think you underestimate the time it takes.
Sure it can go much faster, lets say 1 or 2 years, but then you actually have to work at it. Tournament length games, analysis, books on "boring" stuff like endgames, etc.
Thanks, will try
There ought to be an aptitude test for young children. Save a lot of frustration for the masses.