If that was true, why couldn't Ganondorf just use his powers to get out of the Twilight Realm in the first place. My guess is there probably is another way between the Twilight Realm and Hyrule, that only Twili can access. Much like the wall of twilight that Link could only get into with assistance from a Twili creature.
The reason why Ganondorf could not escape the Twilight Realm was because he was injured and near death (being kept alive by the Triforce of Power)when he was in the Twilight Realm.