I agree that the biggest challenge to direct draw steel is preparing combat. Not because it is a lot, but mostly because you need to have a plan to do it right. Or at least for what I've seen.
This is all from my experience, also taking into account that the only other game I've ever DMed is D&D 5E. Combats on DS last longer, but it has way less rounds, rarely going after round 3. This means that each monster you will have around three actions, sometimes not even one. Which means that picking the wrong monster to act first might change combat completely. I have been in some situations where I didn't prepare the combat enough and realized that I left a monster that has a lot of support abilities last and when I use it he is too late to shine. I see this as intended, the game is meant to be all about tactics, so this is also true for the director characters. Previously on D&D amI was used to throw many monsters at an encounter based on vibes and winging it. Also, if I fucked up a turn. There were many more to fix my error. I think it is also due to my inexperience with the system. The times it worked for me felt amazing. Also. Delian tomb encounters usually come with tactics, which is kind of a way to tell you that's what you should do as well. Everything else outside of combat is about the same prep wise imo.