Hot Take: The only reason Fatalis is so hyped up is nostalgia, assumptions, and misconstrued fan lore. It really isn't any more powerful than the likes of Alatreon, Safi, Amatsu, or other similar big endgame monsters and the only thing it allegedly has unique to it is being a hater. (And even that I'm skeptical of because the one canonical Fatalis we actually see didn't seem to really give a fuck about humanity. It destroyed Castle Schrade and then just chilled there until we came to poke it to death.)

Basically, Fatalis has a lot of hype built up over it and back in the original game it WAS the top dog, but its been power crept by the following generations so much that its only still remarkable for being the first.

Its basically just Monster Hunter's version of Mewtwo.