Apparently. Im surprised thats such a game-changer but I suppose when every stage has the same dimensions aside from the makeup of the underside, there is some merit to the thinking.
In the very least its a debate. Ardent Smashers would say the stage must perfectly replicate Final Destination to be tournament-legal while others say the underside is ultimately not a big deal in actual practice.
In defense of saying the difference can be meaningful, I have seen videos of characters battling intensely below a stage in a desperate effort not to be the first guy to fall down. In a stage with a solid bottom, that wouldnt be possible so there might be a way one character could deal with falling off on a stage with walls that run down to the bottom that their opponent may not. Does this actually matter in the stage selection process? See the previous paragraph.
The only game reviewers who can be trusted are those who publish in Latin or Swahili.