Why are Cloak and Dagger so popular?

They are probably the strategists I see the most, and I wonder why. Her primary healing isn't very strong, she can't keep most allies under fire alive, she needs her special abilities, but they all have cooldowns. As a tank main they are the ones I struggle with as teammates the most after Mantis, they just can't keep a tank alive at full health just like Luna, Sue and Loki can. Although I imagine they are good to heal squishies.

I'd suppose it's because she can use her bubble and turn into a DPS to kill divers and enemies in general?