Those are price categories and not quality ones to begin with and they are not well defined. I'd say <200, 200-700, 700< and maybe some silly summit-fi on top. It makes sense to use them since usually people are coming with a budget in mind and even if in general price doesn't correlate with sound quality it is still true that the good options at a price level are most better than the good options in a lower level. There arr just so many bad ones in all price ranges that the correlation is broken.