I don't think it's necessary or desirable to go through your whole life learning from a single source -- but I think that you do need to give it some time before you really understand what that source is teaching.
I think the whole point is silly and out of context.
I had some prior experience before I met Gleason sensei. I jumped around a bit and I can what you are saying from that perspective. But, I met Gleason sensei in 1990 or 1991. I learned primarily from 1 source for about 18 years. During that time I traveled and learned from everyone else I could and that help me learn from that 1 main source.
What I found was that the 1 main source I was learning from was ME. I am my teacher. Gleason sensei was/is my guide. He set a direction that I continue to follow in my own way. Now I have Dan as another guide. I'm still learning and teaching myself. But I can handle more/additional related advice and integrate it - because I am extremely well trained to do so.
And since I have the opportunity to go share and trade with others who feel the same way, I'm going to do that so that the people I am guiding can reap the benefit. If I am not making sense here, why does anyone ever go to seminars?