First, eggplants and zucchini are fruits too, and both are sweet, just not banana-sweet (in fact, try zucchini bread if you haven’t - best shit ever). Second, many veggies are sweet, like carrots, onions (though it’s masked until cooked), and …uh… sweet potatoes. Third, good tomatoes are absolutely sweet, not like candy but especially the little salad tomatoes aren’t very far removed from a grape, which I think we agree are a fruit. Then there’s olives, that bizarrely savory, dark fruit. They’re delicious but I’m pretty sure they’re from another planet.
So overall I think, if we’re going to go by flavor, then imo acidity is the least ambiguous differentiator. Still not perfect, I’d rather just call it a fruit if it has seeds and isn’t a pod. I’ll give it to you on texture though