Quoted By:
Even Iris has more redeemable quality than Serena. She is mainly hated because --
1. She was the lead girl of Best Wishes
2. Received special treatment like catching a Dragonite for free
3. Trying to make a "Misty" out of her.
4. Her constantly referring Ash as a "kid" when she was even more immature than him.
Misty manage to criticize Ash because she was notably more mature and knowledgeable than Ash while he was an actual rookie. But Ash was an experienced trainer that traveled to 4 region on Unova while Iris was just a newbie trainer with an Axew who just started her journey. It does not matter that she had a winning streak of 99 battle with Exadrill in her village because its still nothing to Ash's four region experience. Not to mention that she kept repeating the same punchline with everybody instead of trying something new. Iris was more similar to Max than Misty since both of them acted like a know-it-all despite not being as mature as they think they were.
However the anime can still fix Iris's flaw and make her a more likable character.