It sometimes is.
The FMGC is based on a prediction/calculation that takes into account the crew inputs.
The FAC works 'backwards' using aerodynamic data to produce it's figures.
There's no real conundrum below 100'.
VLS isn't the end of the world, and indeed is a long way above it.
If you move the Thr lvrs out of the detent below 100', the A/THR disconnects - no big deal really, as long as you know it's gonna happen.