Some sweet potatoes can be very sweet

Yeah, there are sweet tubers. But, you can't put a raw piece of sweet potato in a fruit salad. If you cooked it to bring out the sweetness it would be as sweet as the fruit in the salad, but it would stand out for being very mushy.

Pulses are incredibly variable too in their usage.

I haven't heard the term "pulse" before, I've heard "legumes". But, yeah, that group has a lot of variety. Red beans are frequently used as a sweet filling in east Asian cooking, chickpeas as crunchy snacks, etc.