DBZ is full of plot holes, what's new? The movie was about as good as any other DBZ movie so it was decent IMO.
But I disagree with some of your points:
1. A Legendary title is far below a God title, Broly is non canon and he was also dead at the time, so there is absolutely no reason to bring him up at all even if they knew about him
2. Bills was quite capable of destroying the planet at the end, he spared them because Goku gave him a good fight, that should have been obvious dude.
3. While Whis is flamboyant, there is nothing to suggest he's gay and even if there was I really wouldn't consider it a mark against the movie