The issue is that no-one has a cast-iron definition of what exactly amounts to a measurement, outside of something entangling with the system being measured. Y

The issue is that no-one has a cast-iron definition of what exactly amounts to a measurement, outside of something entangling with the system being measured. You can "disturb" a two-slit system, for example by creating a third slit which will change the "interference pattern" or pattern of probability of detection on the screen, without this being a measurement, though, so the concepts of "disturb" and "measure" are distinct.