MAC doesn't indicate the depth of the anesthesia. It indicates the depth of the paralysis. Which is exactly the problem EEG monitoring is supposed to prevent: In some cases patients can have an insufficient response to analgesia (so they will feel pain) and hypnotics (so they are awake, aware and forming memories) but will respond to paralytics (so they are unable to move and communicate their predicament).

So with this kind of practice, you create any patient's worst nightmare: being cut open, feeling everything, knowing everything, but unable to stop it. And you are unknowing, uncaring or too cheap to prevent that e.g. via EEG monitoring.

Edit: Parent removed his comment. Roughly, from memory, there was some claim by him about being a professional anesthetist, having very rarely encountered EEG and only bi-spectral index monitoring (an EEG-derived computed measurement) in some IV cases, some claims about the unreliability of both and about the preference for MAC (minimum alveolar concentration) to monitor depth of anesthesia.