The head-fi definition of mid-fi and hi-fi seems to always come down to a simple fact of money. People think that if a headphone costs 300, then it's clearly inferior and/or mid-fi compared to a headphone that's 1000. There are plenty of people who would consider an HD650 or DT880 to be a higher fidelity of sound compared to a T1.
Point is that there's good and bad apples no matter the price, and a headphone at a fraction of a price than another can easily possess more qualities that parallel the definition of having high fidelity.
In that matter, comparing the Prime to the DT880/650 is no less offensive as comparing it to the LCD2 and other expensive headphones.