Rotom is not a legendary pokemon. Although you can't breed Rotom, and it has no gender, it is commonly used by some trainers in the pokemon games. This leads people to believe that Rotom is simply a rare pokemon but not a legendary. It can be used in tournaments, has multiple forms, but is at the same standing point as Zoroark and Volcarona. They aren't legendary pokemon, but they are commonly referred as such due to how you get them and so on. Many used to think that Lucario was a legendary pokemon until it became so easy to get
Legendary also means a special Pokemon and also most likely they dont evolve, But the word "Legendary" means hard to get..