Is This Case Structure Good ?

Did you create the case structure given more information beyond the prompt? Or did you just structure it based on your own ideas what might be good?

To be honest, I would've structured it a little differently. Although there's no "right" way to do it here's what my approach would be:

1. The prompt is specifically about how the company can cut costs, so the first question I'd have is "What are the costs involved?" We can ask for total costs and break them down into fixed and variable costs (as per usual) and go from there.
2. Once we know what the actual costs are, we can look at some trends. What is the mix of the costs - what are our most major costs? Have these costs been rising or falling? What services are those costs associated with? As you go, the information given should be able to inform you on which costs can actually be reduced and, if part of the case, can potentially help you calculate overall impact.

So the overall approach I'd take is just attacking the root problem and drilling down to find a hint of the solution - essentially the first branch of your tree. While your third branch might be good to show that you're thinking about everything, I doubt that it'd be particularly relevant to explore in this case because it seems it's quantitatively driven (focused on cost-cutting and possibly profit) than qualitatively driven from a human perspective.

Make sure you support your points with targeted questioning and actual evidence instead of necessarily saying that "cutting marketing expenditure is good" unless you have some actual data to support it.

When it comes to your recommendations, you don't have to write them out, just say them/sum them up based on the evidence. You don't have to specifically mention the framework - you should walk your interviewer through it so they can follow your thought process but don't specifically say "I'm using XYZ framework".

If you want any other advice feel free to PM me.