Been a mercy main for years. You can dish out big healing in the right games and rez is obviously broken. But she just seems outclassed by so many other supports right now. I don’t really know what can be done for her, but perhaps some sort of AoE healing option or a buff to her blaster could help I think.
You are correct she is quite weak.
The problem with suggesting more healing is that the balance philosophy is dmg will always outclass healing. So giving Mercy more healing doesn’t help her position in the game.