You just said it yourself. It's not detectable unless the devs aren't lazy. CheckmateConsidering I work with EAC daily due to my Quality Assurance work, I can tell you right now, it's very much a thing. There's the primary EAC build, then there's additional things you as the developer can request, hence why if you manually install EAC to a game, it'll prompt you to select what game - As it'll download the build matching the game based on developer feature requests.
Not only can EAC scan for file changes and prevent a game launch, it can also do the same for programs running in the background, that a developer has requested specifically be blacklisted.
Disabled programs (sandboxie) was disabled why? It bypasses EAC
The system is set in stone.