> the assumption that, somehow, the logic gets easier to understand if it's in diagrams instead of text

One advantage of diagrammatic/block/flow-based programming is that it lets the programmer avoid fiddly syntax. Many experienced programmers have internalized this to the point that it barely registers as a concern except when learning a new language, but for novices doing things like correctly using tags/brackets/semicolons often lead to more failure and frustration than correctly implementing "hard" concepts like recursion.

For examples, check out the Alice project's papers from Dann, Cooper, Pausch, et al.