so here, you are taking what amounts to a toy and something directly marketed towards children as your shining example of a visual programming language.
in my opinion, labview is the most complex, general-purpose visual programming environment, and people have clearly written rather large, complex applications with it. why isn't it adopted more? a lot of reasons, one of the biggest ones being cost. the other the association with a particular domain, but i consider it a general-purpose language. even if one gets passed that, there is still a huge bias that text is still THE way to program and interact with computers.
well put, couldn't agree more, I often use scratch as an anti example of diagrammatic programming.
visual programming has this topological aspect to it (move a box around and don't change the program), and it demands compatibility with this from the underlying thing, whatever it is, state machines or stream processing functions or whatever.
labview is a great example of a practical use of it, which some relatively minor, but critical modifications you can use it for so many more applications... maybe one day statebox can fill that gap, but we have a lot to do still
Having a language compile to C (as many languages do) does not at all mean that writing in that language is the same as writing in C and that the compiler is essentially just an IDE or for C. Languages, visual or textual, encourage us to think in a certain way. Even though a visual language compiles down to the same thing as a textual language does not necessarily make them equivalent and certainly doesn't say anything about the kinds of problems they help you solve or the type of thinking that they encourage.