> 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.
> Text is the arguably the best way to reason about logic
Math used to be written in prose. Arguably symbols are better.
I think feedback systems are a good example of where diagrams are nice.
All you do with no-code programming is outsourcing writing the actual code to some other company, who already did all the work for you, and you just plug it together. To me, that doesn't reduce complexity, or mental load, it just offloads it to someone else. There's no "no-code" here, they just let you use the code they engineered.