Immersion is whatever keeps you in the game world. Anything that takes you out of that world; anything that reminds you of what you're doing; anything that shatters that good old suspension of disbelief; anything that kicks you out of that escapism for whatever reason is unimmersive. It has almost zero relation to any kind of realism, much less to visuals and presentation — it has to do with expectation. An experience that behaves in a way that you expect will draw you in; an experience that does not will be jarring and remind you that this is a game will do the exact opposite.
Okay sure but even in your definition subjectivity comes into play again because 5 people with 5 different foci regarding their games can feel different about Star Citizen. Ships handling feels like you are piloting a paper plane is immersion breaking for some....others dont even notice. Some people will be very sensitive when it comes to atmospheric nuances (fog, clutter, NPCs) others just want to fly their ships. It doesnt matter if that makes some people superficial, the important thing is that what is immersive is different from person to person so your statement holds true to individual players but can broadly vary when you observe a group of people