Trying to position that ability to hit a relevant target is dubious at best.
Ana is strongest when she’s able to hit allies at about mid range of Q/E with aim down sights (ADS) active. This gives her the space to move forward or backwards with the ebb and flow of the fight without exposing herself too much, in most cases.
In these instances, Debilitating Dart often isn’t in range of anyone, except maybe a tank, which is almost never the intended target for Debilitating Dart.
Increasing its range with ADS would make Debilitating Dart a much more attractive pick, and one that is safely usable on a larger number of targets.
Damage reduction abilities really aren’t too common anymore.
If this is too much of a buff to the old lady (I kinda doubt it is, she was performing at around a 50% win rate before her nerf a while back) knocking the cooldown would be a great place to do it.
Having a more useful, albeit less spammy, ability would be preferred to it’s current iteration.