Finding new clients is something agents do off the clock, and without payment. This is why slush is first read by their assistants, and then screened so that the agent only gets a curated version of the slush pile.
What you're proposing is actually *more* work on the agent's behalf.
Slush *isn't* inefficient, at all. It's a short hand way to get a feel for an author's style, and the overall idea they're pitching. If an agent is already repping a literary rabbit-based epic, then their assistants won't give them more of the same. If the sample is riddled with errors, then the assistant won't pass it along. If the query is for dark academia, and the agent only handles contemporary or cook books, then the assistant doesn't pass it along.
Outliers happen, too. Maybe an agent is tangentially interested in sci-fi, but not specifically looking for it, until someone drops a query for an amazing story with a sci-fi twist that doesn't really fit into static categories.
You're also asking writers to put their unpublished work out in the open where it can be scraped by AI, which is already an issue, but would be worse with this set-up. It also opens *any* novel with a similar premise published after a given project is posted to accusation of copying / idea theft, etc.
If 3 authors post pitches / samples for a sentient tree zombie romance series, and 6 months later an established author's sentient tree zombie romance hits shelves, it's likely that at least 1 of those other 3 will be screaming "plagiarism" online (it wouldn't be, but since when does that matter) because anyone and everyone had access to "their" idea. New / young / unpublished authors sometimes don't understand how long it takes for a book to make it to print, or that sometimes strange floods of the same set-up all hit at the same time. (In general, kids who loved XYZ will grow into authors who write XYZ, so it's cyclical. A few years ago, there was a bumper crop of gargoyle stories, because the authors had grown-up on Gargoyles cartoons, and their stories mirrored that interest.)
And heaven help you if 2 of those similar projects have MCs with the same name, like there aren't a kajillion "Kates" in the world.