Three main threats are Whitebeard, Big Mom and Kaido. Shiki is stuck to the side and in the background
Of course Kaido, Big Mom and Whitebeard are more important. In this panel Oda emphasizes that 3 Yonko were subordinates of Rocks. And, unlike Captain John and the others, Shiki is clearly seen in the panel.
Shiki is grouped with randoms like John and two guys we’ve never heard of
The future Yonko are shown in the big battle against Garp and Roger. Shiki nowhere to be seen.
At no point is Shiki in any way treated as a super legend on the level of Whitebeard and Roger, or even in the same level with Kaido and BM. Sengoku, his supposed great rival, barely mentions him.
He was a decently strong pirate in the past who’s main selling point was his massive fleet. Nothing more. As much of a legend as Don Chinjao was.