I dont think you should think about it as low importance characters dont deserve details. Rather, your comic deserves good art. Simplified human figure is its own important skills too, so I think its worth practicing.
You could use action, composition and layering tricks to keep reader focus on some characters, and transition everything else to vague figures/silhouette. For example, draw a detailed figure of 2 men fighting in the foreground, while in the background, people are less detailed and silhouettes.
This is a panel from my comic. The people in the foreground are the point of focus. Still a lot to draw, but it means everyone in the back are just vague shapes. For most of the back, I drew a few figures and just copy and paste them into different rows. I gradually changed each row's opacity to fade them out. I also layered in some smoke to obscure them even more which helps create depth too.
Also, i planned my comic so that this is one of the important panel so I can spend more time working on it.