She definitely isn't the worst. She is perfectly fine on most defense maps and on some control maps. Her portal is great on big maps, like gamechangingly great. She is also one of the few heroes that can actually deal and with flankers like reaper and tracer. It took me a while to appreciate her damage too. Her charged balls of death do well over 100 damage and go straight through things like Reinhardt barriers, and can do serious damage on choke points or to turrets/bastion. Her left click also does high damage while being braindead to aim. I often kill flankers 1v1 when they walk into me and I'm waiting around the corner fully charged ball on their face then just hold down left click to finish off. You can also flank yourself and take out their back line in an emergency.
Her biggest drawback is that she is not great on attack maps. Portals aren't as useful as your spawn is always close by anyway, and you can't cut off people with kill rooms. I would like to see Blizzard compensate her for that making her a decent pick on attack maps too. Not the best but at least viable.