It doesn't help to ensure anything. But having binaries out there that anyone is encouraged to sign and install, with no way to know what hidden features are there in what projects, is not a very well thought out model if Apple wants to make suckage less likely.
How is it any different than having binaries on the App Store that anyone is encouraged to install, with no way to know what hidden features are there in any of them?
As you well know, upon upload for App Store submission, Apple runs processes that scan those binaries for use of private APIs. Admittedly imperfect processes, yes, but different from having no processes whatsoever.
Yes they are balancing the cost/benefit equation of the untold levels of damage to consumers and to Apple itself potentially done by bad apps on one side, versus the relatively less impactful in their judgement benefits of potentially useful apps on the other side. The assessment that this increases the device's suck relies on an certain assumptions about just how bad the damages could possibly be, assumptions that you make, but that they are reluctant to make on behalf of their users.
