Scything works best when you do it subconsciously IMO. The skill is picked up without even realising it.

I think you word it well when you say that if you aren't scything, you are scraping. But that makes it sound much worse than it should. Using a "scraping" motion has its benefits for beginners - it reduces the chance of cutting yourself (unless you use too much pressure.) It helps you learn good angles and pressure, and lets you know if the blade is sharp enough.

If you start scything too early in the learning process it can cover for bad technique or a poor blade, so it slows your learning.