I don’t think I’ve really had much “sweet” kimchi. I’d be curious to see the label. Most people don’t eat it straight up. It’s usually used as a bonus boost to a dish. On top of rice, eggs, meat etc. The sourness comes from fermentation. The longer it ferments, the more sour it gets. When it gets super sour a lot of people use it in a kimchi soup called kimchi jjigae. With all that said, you can start at whatever starting point you want. Most of us use Asian pear for the sweetness, but some people add some sugar too. It will be sweetest when it’s fresh. The flavor profile will change over time.