Dare I say Ana is probably one of the more balanced Stadium characters? lol.
The issue is not that Ana is weak, she isn’t, it’s that other supports are so much better in comparison. They can spec into survival or mobility whilst still retaining good healing/dps/utility, whereas Ana has to make an actual choice. Ana excels in the first 2 rounds due to how impactful most of her powers are, but once other support builds come online they simply have more value.
Go full attack power, but you are deleted by someone looking at you. Or go full survival and your healing late game is useless, due to scaling. This is actually healthy and in an ideal world how it should be for every character IMO.
However, nerfing the rest of the supports is not the answer and will create more issues than it solves, but you can’t buff Ana either because her 100% anti-heal can be too oppressive without Kiriko present.
Solution: Nerf nade anti-healing to something like 50% from her base kit and give her some form of mobility on cooldown to compensate. As more mobility/dive heroes get added to the roster, Ana will become less and less relevant unless they re-distribute her power from her nade anti-heal.
At the moment you only really have Genji/Reaper who can be a problem in the backline, wait until Sombra, Tracer, Winston, Doom get added and you miss your sleep dart.