Wow, I've always wanted to ask this question. I seem to be a hit with assistants. They email, they've even called (freaky!). They always say they're going to pass my ms. on to the boss ASAP and that's when the crickets start to chirp. I can't wait for this generation of assistants to graduate to "boss." Of course, their mail will be screened by a new generation of assistants--assistants who might hate my work. Chirp, chirp.
I would like to point out that my answer to this is almost unrelated to the previous post because it discusses assistants, not assistants who are in the middle of becoming sub-agents.
In general, assistants do not request material on their own (unless they really push for it, which never works anyway). Even if they sign their name, they're doing it for the boss, because the boss wants to see it. The slowdown is unrelated. It's because agents are busy people and have a lot of other things to do, and so the partials and fulls pile up. I've got partials sitting at agencies for approaching a year now. (That's unofficially a rejection) So don't worry that it's the problem of who the boss has hired. It's a problem of the boss's busy schedule.