Thomas, we finally found something to disagree on.
I agree with Brett, and his analysis of working with one agent. You used Calgary as your example. I don`t know Calgary well, but I think I know it and how the world of Realtors work well enough to comment.
It is not possible for any given Realtor, no matter how good he/she is, to know of every good deal that is going to work its way onto MLS. This may tend to support your argument. But, let`s carry that one more step. You would need to know and have a good working relationship with EVERY sales rep in order to learn of each and every property before it went MLS. That is not practical.
In addition, next to none of those "pocket listings" gets sold prior to going MLS. What a recurring buyer really needs is a well informed Realtor who can give advice on those new MLS properties. Every Realtor now gets notice of new listings that meet the criteria they are searching for, so instant notification is not the selling point it was 15 years ago. We need knowledge and experience as an edge; and most Realtors know their city very well, with few specializing in a given area. (Prior to surrendering my license I did specialize in condos in North Van. But I was the rarity.)
Calgary is not that big that you need a NE expert and a SW expert, etc. Vancouver, as an example, is different, with the North Shore, Surrey, Fraser Valley, etc being its own unique enclave. In fact, the Fraser Valley has its own real estate board, even though you can`t really tell when you are leaving Greater Vancouver and entering the Fraser Valley.
There is no way that in a smaller city, such as Red Deer, one would need two or more Realtors, IMHO.