Jack - personal experience of converting Anything via computer programmes is that they are capable of producing garbage in just ONE step.
You are correct in stating that an experienced ABC transcriber hand coding dots into ABC format will produce accurate ABC much quicker than messing around with computers.
What it would then give is a bunch of ABC files. That doesn't help with the score writing/editing software I use. MuseScore doesn't import ABC, and neither do many other programmes. Music XML is currently a lot more portable between programmes.
I have noted out tunes using ABC, but don't do so often enough to remember what the rules are. I find that four decades of reading the dots makes "lines and dots" music writing a better option for me.
Quack!
Geoff.