To the OP:
No one has ever claimed that Mario 64 was the first 3D platformer. Bubsy 3D and a couple of other games gave it a miserable try first as well. But Mario 64 WAS the first 3D platformer to actually BE fully 3D in it's gameplay, and to actually WORK, and play WELL, and be, you know....a fun game to play. That is why many people refer to it as "the first", because it was the first one to matter, and the one that all others afterwards, Sony included, emulated.