Yes, that is absolutely true. But as I have mentioned before, with my older phones running AOSP or Lineageos it was always recommended to cleanly flash a new major version of Android for the first upgrade. Later, with minor upgrades that was not necessary anymore (i.e. from 10.1 to 10.2), but for example from 10 to 11 it was necessary. There was only one exception with 12L, so from 12 to 12L they also recommended the clean flash.
I clean flash usually meant to clean /system and /data during the process and I guess the adb flash tool from FP does exactly that.