I have mixed feeling on this. A downed character is not necessarily dead so helping them up is useful if they have an ability to defeat an enemy. I don't help a downed character if an enemy with more than a quarter of like is next to them. I try to take them out first. I feel like revivify should bring back a character at full health instead of a quarter health. Helping a downed character can be useful depending when is their turn and if a enemy has low health.
It is incredibly useful to help a downed character back up; that's exactly the problem. It's too useful at too low of a cost.
While a downed character isn't dead, they have taken a possibly lethal would and are in danger of bleeding out. Barring magical healing, other characters shouldn't be able to take a single 6-second action to bring them back into the fight. Even with a successful medicine check, the best they could do is staunch the bleeding. This wouldn't bring the downed character back to fighting fit, and if they tried they'd almost certainly just start bleeding out again.
