That is hardly unique to DMA. Law is rife with things requiring interpretation. See, for example, the reasonable person standard: https://en.m.wikipedia.org/wiki/Reasonable_person
In Apple's case, the edict was to create competition by opening up the app stores. Apple "opened" its app store in a way that failed to actually allow competition and so it is subject to the fine. This is exactly why laws work this way - to prevent what is now called "gaming" the system.
It’s a law that establishes no measurable compliance guidelines, while providing absolutely no limitations on what the EU can decide counts as a violation retroactively. It’s basically “We’re not going to tell you what we want you to do. You need to guess what we want you to do, and fuck you if you guess wrong.”
But my point is that you can't say "just comply with the law" when compliance has been a much more interactive process.