Again, I think you're looking at this too much from the standpoint of an Owner, and not enough from the standpoint of someone who sees this suggestion to rent from one of these brokers in a facebook group, or is told to do so by their friends, who have done it. All they see is a deal and a good one at that...they don't realize they are paying more per point than someone else for a lesser room. They probably don't even realize it's a lesser room than a standard view in terms of size as most rooms on Disney's consumer site are classified based on location (heck, there are owners that don't know the differences between these rooms as that questions comes up quite a bit about the difference between a value and a standard room). In this case, the Value room, while smaller still has a pretty good chance of being in a better location (pool view/savannah view) than a standard studio though.
Just for the heck of it, I wanted to see if I could pinpoint what you were talking about though. It took awhile to find an AKV value studio available on the consumer site, that was in the same range as Rentals on that brokers site. I found one available on consumer site for August 6th and thankfully the rental broker has more than a few value studios around that date as well as Polynesian standard views. These were the numbers I found.
Disney Consumer Site AKL-Value = $464 pre-tax and $522 post tax
Rental Broker Rate for same room = $297 and $309 after adding processing fees (A rate cut of $213 or a 41% discount on Disney Rack Rate...with the broker selling for $33 a point in this instance).
Disney Consumer Site Polynesian Standard View = $698 pre-tax and $785 post tax
Rental Broker Rate for same room = $540 and $563 with processing fees (Rate cut of $222 or a 28% discount on Disney Rack Rate...with the broker selling for $27 a point in this instance).
Just to add some price comparisons from the consumer site as well to compare against the AKL-Value:
Pop Century - $241 ($68 price difference between AKL, which is a deluxe resort, with better pools, a bigger room and a chance at a Savannah View).
AOA Little Mermaid - $294 ($15 price difference)
Coronado Springs - $323 (AKL is cheaper by $14)
Port Orleans French Quarter - $345 (AKL is cheaper by $36).
If another broker wants to rate cut them, I guess they could, but their prices when you really look at them and compare them with rack rates, are way more than fair and already a pretty substantial discount. The fact they are pricing the value the same as a room like AOA Little Mermaid, says to me there isn't that much wiggle room to further undercut that price.