> There are visual languages that look the same as above, but lines are actually dataflow instead of function calls / control flow and the boxes are not opaque functions but introspectable data flow descriptions themselves. These offer some unique benefits...

I've only had a brief (few months) experience with Max/MSP, although I've played around with other visual languages too (SynthMaker and others) and have been interested in the topic of both visual and dataflow languages for a long time. So, with that bit of context, I completely agree with your observation!