Well, that's true. But some of them, such as Milotic/Feebas, Tyranitar/Pupitar, and Gyarados/Magikarp, are vastly different. So they should probably go into different categories. While the ones with minor differences, or those who have traits of the category that the final stage evo is in (i.e. Dratini/Dragonair/Dragonite) could stay in one genre.The problem with the differences in evos, as you have stated, is that it would be too many that have differences to add on.
There may be a Ghost Tier, beings which originated from Giratina.
-Terywj
Sounds good, although Sableye and Shedinja might belong in other categories.