For, say, people like me who aren't afraid of complexity but are put off by certain kinds of resource-gathering, more so if it's in the Nether? Being somewhat realistic is all good, but I think it is not unreasonable to permit tweaking a recipe if it takes more time to set up the logistics for a mid-tier production facility for one fuel type than it takes to explore the rest of the tech tree.
Edit:
Here's what you need for a reliable supply of jet fuel ingredients if you want to stay with RoC as much as possible: a blaze spawner, a slime spawner, a boring machine in the nether, a boring machine in the overworld, the ability to fly (for the ghast tear), an ethanol production facility and repeated expeditions into the Nether to gather soul sand manually. Basically, I'd say without either Forestry and Gendustry or Magical Crops it's not worth the effort and if you're put off RotaryCraft completely by it that's perfectly understandable. You do want people who take an interest in RotaryCraft and are willing to learn the basics to continue to explore it, right?