> Most recent example: I participated in Advent of Code this year, and there was almost never a Racket solution posted that wasn't ten times slower (and in my opinion harder to read) than the simple & idiomatic Python solution.

Can you point me to some examples of this? I haven't done AoC and so don't know where to find solutions posted to compare. It should be very rare for idiomatic python or php to be faster than idiomatic racket.