Ashby's book is pretty decent, considering that Cybernetics as a field can feel unapproachable to lay folk. In terms of DNA, cybernetics and systems dynamics both draw deeply from the well of early control 20th-century theory and so there are some conceptual overlaps. In relative terms I think cybernetics does a better job of surfacing the contributions of information theory and system dynamics does a better job of surfacing the impact of stocks and flows on overall dynamics (as its name would suggest).