Well, she doesn't have anything that allows her to hit hard. Her healing ability is just that...healing. And she has a double attack that she doesn't gain until later on. And even then, you can bearly use it at all. Either because you are using magic that. Most of the time, I am just spamming Celestia's magic to kill everyone anyway. The only reason not to lose Cadence is to make sure that at least one other pony is not fully captured.
I still say that you can for the most part use the drone ability after you beat the first level. Becoming a sort of super solider.