What kind of a thinker would you become if you grew up with an active simulator connected, not just to one point of view, but to all the points of view (...) so they could be dynamically tried out and compared?
— User Interface, a Personal View - Alan Kay
I don't think that the complexity issue (...) is essential. I think it's self-imposed by current visual language designers. Perhaps that's because the handful of visual languages that got traction (and thus the benefit of countless hours of design & development effort) are created for people who aren't computer scientists. These languages only need to be sufficient for solving a domain problem, not for advancing the art of the visual PL.
The fact that current visual languages are built of monochromatic text, a few box shapes, and a few colors of line, is a tremendous failure of imagination.
Secondary notation is poorly developed in the box-and-wire notations we examined, which we believe makes them harder to understand (although as yet, large-scale studies of comprehension have still to be reported). To achieve their aim of making better use of the visual medium, VPLs need facilities for colouring, commenting, grouping, modularizing, etc. (We recommend an explicit 'description level'.) Techniques to reduce the cluttered-wire problem would greatly increase the scope for using spatial layout as a form of communication.
— Usability Analysis of Visual Programming Environments - A "Cognitive Dimensions" Framework
Protoboard nodes by design encapsulate code instead of other nodes, compared to some VPLs where even basic math equations have to use blocks and connections.