The auction is the whole product. A broker who submits a policy to three buyers and a broker who submits it to thirty are both brokers, and both are fiduciaries, but they will not produce the same number.
Aggregate volume is a rough proxy for reach. A firm that has moved billions through the market has relationships with buyers that a newer firm has not built yet. That is not a guarantee of a higher offer on any single policy, but it is a reasonable thing for a policyowner to ask about.