I love this question because it is filled with none other than Snorlax! :o
Snorlax, however, is listed as basic because Munchlax is considered a baby Pokemon. Other Pokemon who are evolved forms that are listed as Basic have Baby pre-evolutions, like Elektabuzz for example:
Also, in the games, you can actually hatch a Snorlax without ever evolving it so it is basic in that way.