I'm sure that's technically true, but looking at the statistics on Querytracker it seems like some agents are a whole lot more eager to find new clients than others. I mean, there are agents listed on QT who claim to be taking new clients but haven't requested pages once out of 500 or even 1,000 queries. Contrast that with other agents who request material off 10% or more of the queries sent to them and you have to conclude some agents are devoting a lot more time to seeking new clients than others.
From my experience, and agent who is requesting queries is looking for new writers, but they can't all want the same number of clients. Not all agents are any good at all, some are just starting out and have no stable, and others are extremely good, and may be looking for only one or two new writers.
Whether it's a solo agent or a big agency, there's a limit on how many writers they can take on, and they know that limit. A good agent has a lot of selling writers in her stable, and usually quoite a few writers who haven't sold anything. Such an agent make be able to take on one or two writers, and that's it. When this is the case, the agent is extremely picky about requesting material.
At the otehr end of the spectrum is the brand new agent who just hung out a shingle, and likely has no stable at all. This agent will usually request material from an immense number of queries in an effort to build a stable quickly. So, sure, some agents are much more eager to find new clients. This is not always a good thing, and it's how too many writer land an agent who, at best, is unproven.
Publishers do not treat all agents equally. Like writers, agents have to prove they can deliver quality material on a consistent basis. Until and unless an agent proves this, she's just someone the publisher never heard of who is sending him material he may hate.
OT numbers are often
highly misleading, but if the numbers there were all I had to go on, I'd go for the agent who very seldom requests material every time.