The whole point of Usopp's Character is to be a Normal "Coward" Person stuck in a Superhuman Supernatural World, what's the point of him joining those Monsters in what They are already capable of doing? To truly make him feel needed, He must shine when others Struggle, so Oda simply creates Characters who Counter such Powerhouses & then portrays Usopp as Solution,
Miss Golden Week trapped Luffy? Call Usopp
Perona counters Luffy? Call Usopp
Sugar gonna erase Luffy? Call Usopp
(Baccarat from Film Gold is also another Example)
What makes these Three Girls different than other Hax Combatants like Hancock or Big Mom is that They don't really like Direct Combat,
Golden Week wasn't a Fighter at all, Perona was resting in her Room & only her Ghost Fighting and Sugar tried to trick Luffy/Law,
Imunko is exactly being Portrayed similar to those Three, so don't be surprised if She is another Usopp Victim,
This Arc started with Luffy saving Usopp & being disappointed in him, so it's not far-fetched to say that Usopp will Save Luffy soon.