In my opinion, the only good piece of advice Iris got during the Junior Cup was Cynthia saying that she needs to work on her relationship with Dragonite. That would have made a lot more sense to bring it up right after the first round, instead of just everyone reassuring Iris that everything was okay, and including that she should use a different Pokemon for the rest of the tournament, but I still think that was the only really helpful bit of advice Iris was given. Although, Iris honestly should have figured that out herself right after the first round and decide to work more on Dragonite on her own, rather than just keep on shouting and crying at it in the hopes that it would actually work. Considering she did pretty much the same thing with Excadrill and that wasn't solved through battling, Iris trying to do that with Dragonite without doing anything different or trying to understand the problem herself does make her look like she learned absolutely nothing from that first problem. I don't think that the problem with Excadrill was solved that well either, but it didn't involve using it in battle, but rather working on her relationship with it off of the battle-field. If Iris had made the connection and decided to use a different Pokemon for the rest of the tournament, then that could have showed some decent development on her part, that she actually learned something through this journey and possibly would have taken action on this problem herself after the tournament.
A part of me thinks that she would still get an undeserved victory from the second round even if she did use Excadrill, but it would have made her look like a better trainer, as opposed looking terrible by continuing to use Dragonite and just hope that the problem would solve itself with little to no action on her part. I really did find her completely annoying and unlikable during Dragonite attacking out of rage. All she did was shout and cry at it to listen to her and didn't even try recalling Dragonite when its attacks were going near the other trainers and the people in the audience. That just made Iris look like she valued winning the match more than the safety of others around her. To be fair, I doubt that recalling Dragonite would have really worked since that rarely works when a Pokemon doesn't listen to their trainer. Even so, it would have put Iris in at least a slightly better light in that she recognized that she was way over her head with using Dragonite and that she needed to stop the match immediately so that people wouldn't be in danger, instead of hoping that Dragonite would listen to her again so that she could still win.
At this point, Iris still looks like she isn't anywhere closer to begin a Dragon Master than she was when she first left the Village of Dragons with Axew. They haven't really done a great job with explaining what a Dragon Master is, although I think it was something like a trainer who bonds with the heart of Dragon Pokemon, but despite BW having over a hundred episodes, it doesn't feel like Iris has made a lot of significant accomplishments to make me think she is any closer to her goal or has made decent progression as a trainer in general.