You are correct, sir.
Because this movie's MacGuffin quest (amid the many other MacGuffin quests) actually contributes to the story. As I said before, this movie does suffer from having way too many MacGuffin quests, but at least they are all relevant to the story. Feels like a video game.

The issue I have with the Canto Bite scene isn't that it's a side-quest, but that it's an ultimately irrelevant side-quest. Other Star Wars movies have side-quests too, and that's fine so long as they all service the story.
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What would happen if Finn and Rose never left for Canto Bite? Pretty much nothing. They still wouldn't have broken the First Order code. The First Order would still have decimated the Resistance fleet. The Resistance survivors would still have been forced to flee to Crait. The Battle of Crait would still have happened all the same. Nothing different.