I mean part of the writing would be working with what you have. If a panel is already drawn, you need to find a way to fit what the story needs into the available space.
If I remember my old marvel comic, these stories are many things, but concise in terms of word count is not one of them. The Marvel method was an assembly line to mass produce consistent comics. I’m certain the artist knew they had to be generous with the amount of empty space in each panel, and it would save them some work.
In my own personal experience, sometimes, I refuse a revision from my editor because the alternate version would take too much space. We then have to come up with a third version of the text that conveys the idea and fits into the space constraint.