They are obviously not filler since they appeared in the manga, but the characters have no importance in the story, that's what I meant. In addition, Blackbeard was also planned early and Oda initially wanted to make him ridiculously strong. In his early concept, he wouldn't be able to feel hot, cold or even pain and his only weakness would be the inability to swim... he would be so powerful that even the admirals wouldn't be able to beat him (in other words, he would probably be the Blackbeard we know with Prime Whitebeard's strength).
BB was the most probable final villain of the series back then and most likely Shanks' rival until Luffy became powerful enough to fight him (the early Yonko would be relevant too, but Kaido and Big Mom weren't among them... it's even possible that Oda decided to go with the Shichibukai, but by Enies Lobby he decided to go back to his Yonko system).
Since the Drum Island Arc, where BB was first mentioned, was released back in 2000, the sketches below might be from the late 90's.
This piece of text (probably an interview with Oda?) has info from differents years (some are literally a decade apart). For example, the Shichibukai's creation happened very early, but, if I'm not mistaken, Oda decided to create the Supernovas after a last-minute editorial advice (namely, when he was already writing the Sabaody arc). It looks more like he let slip a bunch of unplanned things at the same time (doesn't look like an exhaustive list), we can't determine if the Yonko would be the final villains with just this.
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They probably sent out the fodders first, you know the
modus operandi of the marines.
😂