I personally enjoyed this movie. Please no hate.

Ok, first off, where were the Egyptian Gods in all of this? What happened to 'Infinite Power Obelisk'? The Gods would have smashed Paradox's measly Malefic monsters.

Secondly, this whole thing could've been avoided if Paradox had done either two things.
1. Go back in time to when Pegasus hadn't thought of Duel Monsters and kill him.
2. This is more drastic but go back to Ancient Egypt and destroy the concept of Duel Monsters.
Both would've resulted in the 'Grandfather Effect', if he destroys Duel Monsters because the world was going to end, but the world didn't end so he wouldn't have destroyed Duel Monsters, but since Duel Monsters exists, the world is going to end so he has to destroy Duel Monsters- Yeah, you get the idea.

Thirdly, why the hell was Paradox in Venice?

You also got to remember. It's a kids movie, and they're gonna do whatever the hell they wanna do with a movie.