how are iwabe sumire and shinki more prominent than sarada?
Because unlike the Main cast, these side characters are more prevalent of their own with goal oriented and BG lore they can bring to the story rather than to be completely dependent on Boruto.
Sure Sarada goal to become Hokage is vital part for Boruto to become hokage supporter but the way I see it, Sarada goal is always centered around Boruto. Sarada hasn't shown any plot relevancy that pertains to her story arc since Gaiden and when does get developed, she only contributed to Boruto rather than her own. Sarada goals leaves more skeptical because the writer havn't explain anything as to why she wants to become hokage in the first place.
Iwabe and Sarada shares common goal and yet Iwabe had more character depth because we see him struggle to become a better shinobi and his failures is catching up to him. He's suffering from being repeater and he tries to aspire to be acknowledge by everyone. There is promising potential in Iwabe as soon as Naruto was the person to interact and relate with him which is something we don't normally see in Boruto for secondary characters to get this much treatment.
We see Sumire moved on and striving to become a scientiest which is basically following her father footsteps. Her roles as a scientist connects the main theme of the story which is technology. Also Going by the narratives, it told us the fact that The Gezzou Tenou on Sumire was not resolved which speaks volume of her importance and future potential she can bring to the story. So far Nue act correspondence on the Joagan and Hanabi is looking after Sumire who happens to be Boruto Aunt.
As for Shinki and Kaweki, they are rival to Boruto so I don't really need to explain.