I have my doubts that the "visual" aspect is as important as the creators of such software tools would like everyone to think.

I strongly suspect this is highly personal. People can relate to thoughts in different ways. The developers might primarily 'see' argument structure in their heads, where you might think less visually. This tools helps them clarify their ideas and show them to other visually oriented people.

So you're right that it might not catch on, but it may be that the visual aspect is hugely useful to the people it's adapted for.