That's a fair point. And, frankly, it's most of the point of starting at the agency as opposed to, say, starting out directly as an assistant at a studio (a shorter path, but one that yields far fewer contacts outside of the particular studio you happen to be starting at). Even if you don't want to be an agent, starting at an agency usually yields a better career ROI than starting on a desk at a studio or network (or in, say, something like the NBC Page program).

Plus, as I mentioned, there are the resume benefits that accrue with having done time at an agency. "Agency experience" in Hollywood is a little bit like "McKinsey experience" or "Goldman experience" in other industries. It's highly valued as a general indicator that a) you have a very solid, holistic understanding of how the entire business works, and b) you can handle high-pressure environments (provided you lasted at least a year, and preferably two, at the agency -- ideally with some indication of upward movement while there).