Ah, sorry, that was a confusing choice of words. In the law they are using "effective" to mean "has the effect of" not "works well."
In any event the entire phrase "effectively controls access to a work" is defined in the law so what the words mean in english is irrelevant.
Here it means anything that "requires the application of information, or a process or a treatment, with the authority of the copyright owner, to gain access to the work." Which I think we can all agree is very broad.
Ah, but it isn't the copyright owner putting it in place. YouTube is. Therefore, it's just a protocol quirk of speaking YouTube.
You can say it's a selling point meant to entice ordered an the pot for rightsholders, but frankly, there is nothing but bandwidth consumption, storage, and processing limits that keeps anyone from just fuzzing the CDN namespace.
Stop thinking keys to locks. YouTube isn't there for that. I can pull off the equivalent of driving a fleet of minivans up and walking out with copies of the drives if no one else is eating up the bandwidth for long enough.
In any event the entire phrase "effectively controls access to a work" is defined in the law so what the words mean in english is irrelevant.
Here it means anything that "requires the application of information, or a process or a treatment, with the authority of the copyright owner, to gain access to the work." Which I think we can all agree is very broad.