Yes, this is a good point. Lucio and Mercy are kings of reliability since they don't have to divide their attention as much. Ana chooses between healing and damage, has to keep LOS, has her grenade and a sleep dart and doesn't self regen so after a few hits she has to seek cover which isn't as easy as with Mercy.Ana can heal more, but is less reliable. Since you actually have to aim and reload. People move unpredictability at times so not all of your shots are going to hit. However, Ana can heal at much longer distances and can switch easily between healing and damage. Mercy has better mobility and can seamlessly transition from different targets due to her instant beam. Her ult is also still very good and one of the best in the game.
They both have their pros and cons. I still see Mercy being used more than Ana. However, for the most part I see a lot of Lucio/Zen combos.
Maybe Mercy could use a slight healing boost (the current meta is super aggressive so slowing it down could be desirable) but I think the trade off between reliability and burst healing is pretty good. Supports mostly seem to be in a good place right now, with Lucio and Zen being maybe slightly too powerful but eh.