My understanding is that technically DRM doesn’t really need to work perfectly to achieve its objective. DRM works in conjunction with anti-circumvention laws.
Making a private copy of a copyrighted material is legal in many jurisdictions, it is however illegal to circumvent DRM. So effectively by protecting content with any reasonable DRM, the content owner gets more control on the user than copyright law give them. Without DRM you could subscribe to a streaming service and legally record all the content without infringing any copyright. With DRM you are forbidden to do so and anybody helping you doing it is in hot waters: end result no equivalent of a VCR for the internet era.