Unless I'm reading this incorrectly, that would actually make your point moot. According to your statement they didn't get to his level and then they went back to something else. That isn't my experience and I wouldn't agree with that statement.
Let me rephrase: relating previous or concurrent martial arts training (or lack of it) with surpassing O Sensei has no point as we can say noone reached his level, much less surpassed him.
Of course, if someone has reached or surpassed O Sensei is debatable and opinions may vary, surely for some this has happened and for some this could be seen as heresy.
Like everything, it depends.