Akira Toriyama's goal for introducing Brolly was to show that Brolly is THE Legendary Super Saiyan. So it's quite obvious that Brolly's transformations are much more powerful than those achieved by Goku, Vegeta, and Trunks. The Budokai game called it "Legendary Super Saiyan" to let the players know that Brolly's Super Saiyan transformation is a lot different than Goku, Vegeta, and Trunks's. As I said, Brolly gains incredible size which Trunks does not come even close to reaching. You all must understand that Akira Toriyama stated in an interview that he was rushed to make a episode a week also he admitted that he rarely looked back at what he previously drew (which you see numerous mistakes). So who knows.
Games might be wrong, so can the series. Just like with all these dubb/sub conflicts. Only way to officially find out whats going on is asking Akira Toriyama since many of these companies and fans translated this series based on their own personal knowledge of the language. Including with tons of editing of content also made it hard for a person to follow the series. One of the main reasons they are reduing most all of the audio in the early DragonBall Z sagas.
Also the movies do not in any way take place any time at all in the series. They are meere side or what if stories. Including the so called "OVA" which was just a collection of in-game cinematics. Such as the Garlic Jr. saga... which was nothing more than a filler saga based off the movie. The only movies that have strong connections with the series are the specials. The History of Trunks, Bardock: Father of Goku, The World of Dragon Ball, etc.
All in all, Brolly was very "unique" and he also fitted the legend. "Super Saiyans tend to be violent" which Brolly showed numerous times (He destroyed galaxies for god sakes because he was crazed with his power). "Super Saiyans are supposed to ruthless killing machines" which Brolly definately showed numerous times, just that he toyed around too much instead of finishing his opponents off.