Where is it stated that he was the 3rd in command?
Anyway Xebec, Roger and Garp will take the main spot along with Garling, then you can expect Kaido and BM to take more panel than shiki cause they are way more notorious in the manga, BM could very well be stronger than shiki. Then there are guys like Ray, who for sure will get more focus, and then there is Bogard who could take more or equal screen time, maybe he could compete with Scopper too for focus. In the end there are also captain John, Silver axe and I forget if there was another one lol. Shiki really will not be anything special in that flashback, don't set yourself up for a delusion (if you care like the OP).