If Shiki was anything special he’d have been more than an afterthought in the chapter where Sengoku explained who the Rocks Pirates were.
He is, in the actual manga, an irrelevance. He’s a guy Oda had ideas about, but never really managed to stick him into the story, and instead got put in a non-canon movie where he was beaten by pre-skip Luffy. There is not a single thing in the actual manga that suggests he was part of some legendary triumvirate with Roger and Whitebeard. Instead, he’s only slightly more important that Captain John- and apparently less in the fight against Roger and Garp than an apprentice, non-DF, Kaido was.
Chapter 0 is of very questionable canonicity, given that the last two pages lead directly into the movie which never happened in the manga, and it has never been reproduced in the volumes. You can buy every volume of One Piece and never read Chapter 0.
And Databook Blue was not a particularly accurate databook
His greatest fighting achievement- if canon- is to completely outnumber Roger, in a sea battle, where he had a very broken DF power, and still end up with a steering wheel rammed in his head while Roger got off scot free. Roger’s ship was in more danger than he was.
And to throw a ship at Marineford and get tossed in jail.
A myth of a legend which only exists as a desperate attempt to make a Naruto style parallel between Luffy/Law/Kid and Roger/Whitebeard/Shiki, which does not exist.
He’a strong, but there’s no reason to consider him in the same light as Roger or Whitebeard, and very little to put him above actual successes as pirates like Shanks, Big Mom, Kaido and Mihawk.