Learning how to compile packages manually it was a common skill long before Linux came to be, and how GNU/Linux fits together could also easily be learnt with Slackware or Yggdrasil.

None of that requires LFS; I compiled KDE via scripts many years ago. Why would LFS be needed for that? That makes no sense. Debian being slow is their problem, other distributions aren't snail-like like that. The default compiler used in LFS is also hardly a real cross-compiler, it is more a bare-minimum compiler for C/C++. This annoys me because e. g. I need fortran for R, so a bare-minimum compiler isn't as useful as a more feature-complete GCC. And GCC also causes some issues, e. g. like my problem with options.cc.

I think you missed the main argument though - LFS isn't quite as good as it could be. That is a correct statement that was made.