It seems like to write a tool that's genuinely helpful for non-experts, you need to become something of an expert in how people use the tool: what are they usually trying to accomplish? What are common mistakes?

It's similar knowledge to what you would need to write a book about rsync.

And the way to do that is with lots of experiments and user testing. A good start would be to find one person who really wants this and make sure it works for them. Designing things by yourself, even with lots of sympathy for the user, doesn't seem like enough?