Since there a lot of people who claim Iris received zero character development and progress in her goal, I thought I'd make a post here to show why that is not true.
Let's begin.
1) The first notable piece of development comes from her first Pokemon, Drilbur. Yes, Iris wants to be a Dragon Master, but that doesn't mean is she is forbidden from catching other Pokemon. Excadrill's disobedience is a special type of disobedience. All the other types of disobedience we previously saw in this anime was due to Pokemon growing too strong and failing to acknowledge their own trainer. With Excadrill the situation was different. Even after Drilbur evolved into Excadrill, it fully obeyed to Iris and it wasn't until the battle with Drayden that Iris and Excadrill's relationship suffered. Iris's lack of care for Excadrill, pressuring it into a battle with Haxorus, a battle it clearly couldn't win was a sign of immaturity on her part. Excadrill closing itself off from Iris was both due to shame and its trainer's actions. Iris never really tried to understand Excadrill and she always assumed it wasn't her fault, until she shared the story with Cilan.
Cilan's valuable insight allowed Iris to realize that it was her fault and went as far to apologize for her actions, begging Excadrill to forgive her, saying he wouldn't even have to battle for her ever again as long as it meant they could be friends like they used to and that she would be considerate of its feelings in the future. That moment showed a lot of maturity on Iris' part as well as Excadrill's. Iris took the first step and admitted her mistake and Excadrill decided to learn Focus Blast as a sign of forgiveness. It was simply a beautiful moment.
The whole Iris and Excadrill storyline gets a neat resolution in Iris's battle vs Drayden where Excadrill manages to knock out the same Haxorus it lost to in the past thus bringing the story full circle.
2) Iris progressed a lot as a Dragon Master and as a trainer on her journey through the Unova region. First of all, her Axew, initially incapable of properly using Dragon Rage, managed to master the move with Iris's guidance and became a capable battler later on in the story, learning moves such as Giga Impact. A far cry from the baby it used to be. Yes, Iris was given a goal of raising Axew into a Haxorus, but since when are our main characters allowed to achieve their goal within their respective series? As far as I recall, none of the characters achieved their goals, so why is Iris getting so much flak for not achieving hers? Especially when it was already revealed by one of the animators that Haxorus would be difficult to constantly animate so they chose against evolving Axew.
Then, Iris is allowed to demonstrate her knowledge and gain more experience as a Dragon type expert as she travels through Unova. First she encounters a girl called Emmy whom she helps with her Druddigon. Due to her knowledge about dragon types, she manages to help an inexperienced trainer with her Druddigon. This is one of the first steps Iris makes towards becoming a full-fledged Dragon Master as she begins to work closely with other Dragon types.
Then there was the lonely Deino episode, where Iris recounted her memories from her past in the Dragon Village in order to help a young dragon overcome its shyness. She succeeded in doing that and managed to get Deino to open its heart to her. For a trainer who's aiming to become a Dragon Master, this also was a significant step in progressing towards her dream - she is helping more Dragon types and trying to understand them.
Probably one of the biggest pieces of Iris's development comes from Dragonite. First, let's talk about the Dragonite episode. It was such an amazing Iris episode where she showed why she deserves to be the Dragon Master. She went out of her way to protect and defend Dragonite whom no one would trust, when everyone accused of doing something it didn't do, when everyone wanted to take it down, Iris stood in front of it protecting it. Iris absolutely deserved to catch that Dragonite, and I will never understand anyone who says she didn't.
People say she should have caught a smaller dragon and evolved it...and I'm like...why? Mix things up a little. Thankfully, the writers did just that. Iris got a badass Dragonite, but of course, this came with a proper disobedience storyline. What better way to test Iris's potential as a Dragon Master but to give her an enraged Dragon with poor temper that loses control and lashes out when battle isn't going its way? The whole Dragonite storyline gave Iris A LOT of experience in dealing with a Dragon type like this and essentially allowed her to grow even further as a future Dragon Master.
Then we reach the climax of Iris's storyline when she returns to her village and a Zweilous loses control after evolving into Hydreigon. Iris uses her entire team to corner Hydreigon, then she jumps onto it and manages to calm it down. How do people not count it as progress in her goal? Obviously, Iris does not collect ribbons/keys/badges so stuff like this has to count, right? All these moments with different Dragon types, all the different experiences she gained during the region contributed towards her growing potential of becoming a Dragon Master. It's so plainly obvious.
In that same climax, where we learn about Iris' previous school life, we learn that Iris once battled with a Fraxure belonging to the school. Back then, Iris made a similar mistake as she did with Excadrill, she failed to recognize the Pokemon's state and pushed it to battle despite being incapable to go on further. Iris admits her mistake and apologizes to Fraxure after so many years, she owns up to mistakes that she made when she was younger.
And then we have Iris battling two Dragon type experts, Drayden and Clair, again, valuable experiences for an aspiring Dragon Master. And in Johto, Iris again gains more experience for her goal as she manages to track down a rogue Gible causing problems in Blackthorn City by managing to understand the cause behind its behavior. She also catches it, making it yet another Dragon type Iris owns.
3) Iris's whole storyline is just so compelling. One of the best parts about Iris is that you know nothing about her when she first appears, but as the story develops and more flashbacks are shown, you get to find out everything about her; her dreams, her fears, what she experienced as a child, what experiences led her down the path she's on today. Contrasting to Serena's flashbacks which is all about Ash saving her, Iris's flashbacks are so much more meaningful for her character and goal, majority of them revolving around Iris's experiences with other Dragon types or watching others interact with Dragon type Pokemon. And then Iris's whole inability to fit in with the rest of the crowd at the Opelucid Academy when she was a kid is a reminder that her story is just so much more deeper and sadder than most of the other female protagonists. The sad part is, people overlook or deliberately ignore that because, OH EM GEE, she called Ash a kid. What a b*tch.
4) Emolga admittedly does not add a whole lot to Iris's whole story, but it still contributes something. Aside from having an amazing personality and interactions with Ash's Snivy, we get an episode where Emolga temporarily joins Team Rocket because Iris gets mad it because she thinks Emolga did something wrong. After it is revealed Emolga didn't do anything wrong, Iris apologizes without any issues, further showcasing the growth she underwent since her early BW days where she would blame someone else rather than herself.
There is so much more I could talk about, such as the fact that Iris didn't actually "hate" Ash, that she realized his true worth as a trainer in episode 4 when he saved a hungry Tepig, that she was a true friend such as in the battle versus Roxie where she passionately cheered for Ash and even forced Cilan to dress up with her so they could get Ash out of his crisis, but then I realize, all of this is pointless.
Because no matter how much I talk, no matter what arguments I provide, no matter what canon events exist to prove my arguments, haters will disregard that and call her a b*tch because she has an annoying catchphrase. I mean, sure, Iris is not perfect, but she's so, so far away from being the worthless character you all try to portray her as.
And ultimately, I am just sad that the majority of the fandom will not recognize Iris for the character she really is but will continue to demonize her, bash her and twist her into a version of a character that she really isn't. It's sad and pathetic.