They really are not deterrents.
Even if the unscrupulous entities cared about the license, they would just get their (already paid for) CAD person to reverse engineer every single necessary model over the course of a week. If an amateur like me can reliably do that in his spare time, imagine what a professional could do during an 8 hour shift.
But it doesn't matter either way because no unscrupulous entity is going to be dumb enough to publicly announce that they used the models to produce their clone.
If I manufacture a clone of a Prusa, there is no way for anyone to prove that I used the original 3D models. If it were possible to prove that, it would also be possible to "prove" that I copied 3D CAD models that I've never seen, which could put me in legal trouble. Reverse engineering is not a crime, and reverse engineering (and all the costs associated with manufacturing and prototyping[0]) likely _can_ reproduce a near identical Prusa printer.
As an aside, if you've seen the average Prusa clone, it's often quite far from the original design. Almost nobody 1:1 cloned Prusas back when that was a thing, because the Prusa design didn't cut corners. Those clones would often use designs which were probably derived from the original, and were unpublished. Why didn't Prusa go after them for this? He should have had just as much luck given that those manufacturers were potentially in breach of the GPL.
In summary, the OCL cannot actually stop clones, because if it did, we'd have some serious problems with our legal systems, prohibiting perfectly legal reverse engineering (irrespective of if the cloners did the reverse engineering or not).
It _only_ stops people who are honest enough to state that their designs are derived from Prusa's models. People who weren't a threat to begin with, and who now are voluntarily subscribing to legal issues if they ever felt like selling a Prusa modification without Prusa's approval.
The real deterrents are:
* Design complexity
* Extreme amounts of competition (almost nobody would buy a prusa clone these days unless they _wanted_ to have an almost broken printer to force them to learn how to make it work reliably). We have cheap, good, first party 3D printer designs.
[0]: To clarify, when I say prototyping, this needs to happen irrespective of if you reverse engineer or not. Once you have the models, which will be true to life, you still have to "reverse engineer" the tools/dies/materials/etc, for which Prusa sensibly does _not_ offer the models.