Why The Dragon Ball Z Movies Aren't Canon
As a child, I remembered watching four Dragon Ball Z movies which were edited into two movies. One was called "The Greatest Rivals" which was a combination of Cooler's Revenge and Return of Cooler. Another one combined both The Return of Broly and Bio Broly. I didn't even realize that these movies aren't canon if you try to look at even at the minor details. Please remember the Dragon Ball Z specials like Future Trunks' backstory and Bardock: the Father of Goku are TV specials. Let's get on shall we?
So what's the purpose of the Dragon Ball Z movies? It seems to be a series of what ifs. Let's think of some interesting what ifs that were created by these movies. Here's what I could name of what if scenarios that were made and here's the only ones I'm familiar with... and let's think of these entries like the "What If" comic series by Marvel Comics:
I pretty think that Turles just can't fit in. The events are pretty much a what if scenario if there were more Saiyans that survived Frieza's genocide and Turtles was portrayed to be one of Frieza's minions who defected. The movie could have fit in if the events happened after Frieza and Goku turning into a Super Saiyan. Judging by Goku's abilities where he can't turn Super Saiyan and the presence of everyone who should have still been dead (Yamcha, Chaotzu, Tien, Piccolo) all make the movie unable to fit in. Also, if Goku went Super Saiyan I think Turles would have been ashes and this non-canon film wouldn't exist.
This is pretty much a scenario where, "Should Goku have already learned to be a Super Saiyan?" The whole "False Super Saiyan" scenario also proves that this movie isn't canon. Need I mention that also Goku here uses a puny Spirit Bomb to defeat such a powerful foe? For this movie to be canon, I think Goku should have gone Super Saiyan to defeat a Namek who's that powerful.
Okay he does look Cooler than Frieza but he's not canon. So it's safe to assume that maybe Frieza is King Cold's only child in the canon. He's pretty much what if King Cold had another son. His power itself proves that there's some inconsistency. Remember, Frieza stated that his fourth form is his true form (which Resurrection of F may also be non-canon and more of a what if scenario) and that the first three forms were created to suppress his high levels of power. Another inconsistency is that Goku now had easy mastery of the Super Saiyan. Cooler angering Goku would have already triggered the Super Saiyan power. What's also disappointing is that Cooler's final form ended up getting wasted when Goku became a Super Saiyan. That alone makes Return of Cooler another what if scenario, it fits well with the movies but not the Anime series. His cameo alone in Dragon Ball GT already proves GT to be an alternate continuity.
The movie seems to be set in a lot of what ifs. The movie felt like it was an alternate continuity where Cell is defeated, Goku lives and Android 13 is actually a remnant of Dr. Gero. If it were trying to fit in so where are Android 17, Android 18 and not to mention Cell in all of this? Also, Gohan not going Super Saiyan here fells like it's what if his ability to become one didn't come until later.
This is yet another what-if scenario if you have an Omega Level Super Saiyan like Broly going on. Broly had a total of three movies which fit with each other but not with the series. The movies are supposed to happen during the Cell saga but if it were so, where were Cell, 17, 18 and other important characters in the Cell Saga? It would have been cool if this Omega level genocidal madman could have ran into them. But again if he did Cell would have been totally obliterated by him. The androids would have been destroyed by him. Just the first movie alone already dismisses him from the canon. If Cell did get some of his DNA then I think either Cell will explode or would have become even stronger than before. Too bad his concept isn't even in the Anime.
While you can still enjoy these movies but these are just a series of What Ifs. In short, it's trying to expand the imaginative realm through What If events rather than rely too much on canon.