Red onions are definitely not sweet and they definitely taste oniony.

I have eaten plenty of pungent red onions, I don’t think the color is enough to tell.

Pungent onions, cooked, are much sweeter and more flavorful than sweet onions cooked.

Sweet onions are fantastic raw, but should be called Mild Onions instead.

White onion for cooking, sweet onion for raw, red onion splits the difference, but red onion quick pickle is better than any other onion pickles.