DBGT shouldn't be considered in any argument really since it's no longer canon. And in actuality by just watching DBZ KAI (which takes out all the useless fillers which are not canon) and simply the two movies ( all other movies are non canon) a person can indeed get a full grasp of Gokus power. Also DB, while a good series, doesn't add much to the Goku were referring o since much of DB Goku carries over to DBZ.