Like most things in Bonsai, there’s definitely subjectivity to the equation, plus an artist’s body of work/style. It’s no secret that Ryan’s tool kit uses 3 main techniques for aging a tree, one of which is asymmetry. But unlike others, he most definitely moves to a more committed asymmetrical push, which would explain his point regarding breaking lateral boundary on round pots(which is the strongest symmetrical shape). Oval pots have the play of “off center” positioning to help with asymmetry but he’s mentioned in the past that planting off center isn’t a tool he likes to use(which brings us back to the point above).
Do I agree with his point? For the most part, yes. But like everything else, it also depends. A formal upright, even with an asymmetrical design, might be hard pressed to break the lateral boundary(think chokkan style Hinoki cypress that tapers from a wide base).