The monsters in the Florian Triangle aren't ever gonna be revealed. Their role is that of the classic ending trope typical of thriller movies where is it revealed that the TRUE menace is still out there or it wasn't what it was thought during the movie. After they part from Thriller Bark is it finally confirmed that the main cause of the disappearance of ships wasn't Thriller Bark itself, but those big ass creatures which Oda goes just as far as giving them a vague description without revealing how they look:
"It is fortunate that the white mist hangs over today, as well…. concealing the sea's bizarre face with a white veil". I don't know how the fandom reacted to this since i didn't read forums back then, but to me this is pretty scary. In that page you can see them compared to Thriller Bark which has the size of an island, they are waaaay bigger than Oars. And revealing them would be just as revealing and ruin the mystery of the Bermuda's triangle in real world.
The pictures are showing fog, shadows and light on top of the shadows. Pretty much what you would expect if there are more giant beasts.
I think the basis of the florian triangle theorie is, that the red line is man (devil fruit) made.
If so, it might have been to reduce the amount of "beasts" / "sea kings" someone had to fight. As I mentioned earlier, huge beasts like that are weak if not protected and in small numbers. So if someone was able to separate Zunisha and a couple of others the "ancient weapon" could have been defeated.
This theory would explain the red line, as well as explain the fog with shadows and beasty eyes in the florian triangle…
Oh, and I would like to see the red line be destroyed anyway, for Laboon.
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I didn't mean to say that other series did their final arcs completely right lol. But One Piece is looking much more balanced than them overall.
Like Dragon Ball without the Z