Sure, everything can be hacked into a video on the web. But luckily that makes your web page unusable, unaccessible, and also un-SEO-able. It would also require you to have expensive DRM authoring tools to have you actually create DRM signatures (it's not just a switch you can flip on). Let me rephrase: EME can only be practically applied to actual audio and video.
The point still stands. EME has been commonplace for three years now. If the fear that it would grip beyond audio and video in the real world is based in reality, we would have seen it by now. The W3C decision changes nothing for the people who would use it.