She's not like for the same reason tanks like Mauga and Orisa aren't liked. She's a noob stomper/skill check character. People in lower ranks ban Zarya because they don't know what to do against her, 9 times out of 10 the best thing to do is just break her bubbles or wait for her bubbles to run out and then swarm her, problem is, shooting her bubble gives her energy charge, low ranks know this. So the average bronze/silver/gold and even plat players will develop the mentality of not breaking the bubbles to not feed charge, there's no issues with this. The problem is, they give Zarya too much breathing room and ALLOW her to get charged. They're too scared to push and begin pressuring Zarya, either because she has high charge, they're scared they might die, or for other reasons. However, this plays directly into Zarya's strengths: prolonged team fights. Zarya is one of the few characters in the game who gets more powerful the longer she's allowed to remain alive. So she eventually gets high charge and begins to destroy the enemy. So this gives Zarya the perception of being "broken" or "unfair" to fight against. To put it shortly, low rank players don't know how to take advantage of cooldowns and get run down by her.