This is true. At the same time the Soviet Education Ministry recognized the fact that many schools and teachers are sub-par, and they went to great length to create books for self-study. Math text books curriculum was curated by Andrey Kolmogorov [0] himself with the help of talented stuff. There was monthly Quant magazine (STEM for high schoolers) and a "Quant library" -- short books written by math/physics/chemistry experts for the high school audience. This was very helpful for smart kids that were not in Moscow or Leningrad (now Saint Petersburg).