What's all this talk of nerfing Zarya? Her bubbles are a long 10 second charge, the beam for her gun is low range, the alt fire is very slow and to keep her charge up you have to have good situational awareness and constantly bubble under-fire teammates.
Her main perk is her 200 hp 200 shields. Fully charged she's dangerous, but as noted it takes effort to get there and even more so to keep it.
Her ult is one of the strongest in the game but only when combined with teammate coordination. On top of that it takes a long time to build.
I main Zarya, because I like her play style. I find other characters easier to play though.
She's not even difficult to handle. If you're attacking her, stop when she's bubbling and stay mobile. She has very little mobility and she's rather large. Just keep mid distance from her to avoid her beam.
The only character she has a large advantage over is D.Va. This is mainly because a lot of D.Va players don't know/notice that Zarya's beam goes straight through her defense matrix.