It does take some time. Especially when compared to low prep games like Spire.
However, my GMing has been influenced quite a bit by Blades and Spire, in particular. Even when running D&D. I design a loose scenario much like I would for Spire. I don’t stat up all the participants, but i stead use existing stat blocks (except for truly rare NPC villains). I don’t map ahead of time. If we’re playing with a battle map and minis, I draw the map while my players determine initiative.
So all in all, while the prep is a bit more than a game like Spire, I think it’s much closer to that end than to the kinds of expectations many have cited in this thread.