There are a lot of things about Ana that were hurt in OW2. First off there only being one tank means less shields and bodies on the field. Tank hit boxes are huge and between that and shields it was harder for Ana to land her shots, you could easier body block her heal targets with a tank or shield.
The Role passive also means one of Ana’s greatest weaknesses, no self heal beyond wasting her nade is basically removed as well.
The over all healing nerfs to Support also made Ana stronger as her nade still doubles healing, making her about the only hero able to heal a tank in a decent amount of time from low health.
I will say I don’t really think Ana is OP per say, just all the other hero’s been nerfed pretty hard while Ana avoided most the changes. It’s not exactly that Ana needs to be weaker, just the other support hero’s better.