Consumer laws override what any dealer "thinks". Personally I don't give a damn what they think.Either way, I've had both wheel wells packed with slush and blasted our with a hose with no issue,,,, so far.
We will all agree there are to many unknowns here but either way the part (over stressed/ under engineered) would not of been covered by Mazda/the dealer as already stated by the OP.
I dislike that the liner is two pieces and split in the center. Should of been one piece.
The vehicle must be fit for purpose and in this case it was not...period.