1. Like i've said before neither Ash or Pikachu make up the loss. Everything goes downhill from this point with Ash performing worse in the next two tournaments he competes in and coming up poor in the league. It made Ash look weak and amateurish and worse it made his Unova team Pikachu include look weak and inexperienced, which is a really big shame because most of my favourite Pokémon were in Unova. Compared with DP where he one at least one major non-league competition it's rather sad that he should loose an unimportant contest to a relatively inexperienced trainer using a Pokémon that a few episodes previously didn't even trust her.
2. Nothing is actually achieved or gained from this competition. It doesn't showcase how any characters have grown or developed over the series except possibly it demonstrates a patch up in the relationship between Iris and Excadrill. And that wasn't really highlighted so what's the point - It just makes the arch seem like a pointless filler.
3. Of all the people Ash could have lost against he lost to Iris, who had spent most of the series prior to this demeaning him and calling him a little kid for making simple mistakes. All her victory does is vindicate her and make it seem like Ash is an incompetent and inexperienced trainer and gives Iris more ground to to demean him. That casts a shadow over his entire journey in the Unova region and makes it look like he can't do anything right or achieve anything in his own right. She even mocked him and called him a kid over Pikachu using thunderbolt at the start of the battle, which I think is kind of arrogant.
In any case up to this point Ash has travelled through four regions and managed to gain a high ranking in regional Pokémon leagues and has captured and trained many different Pokémon. Iris had only spent a short period of time as a trainer and had only caught 4 Pokémon by this episode. Ash has done well by showing friendship and respect for his Pokémon whereas Excadrill up until a few episodes ago refused to even look at Iris because she had hurt his feelings. For the two of them to turn that all around and come out with such a massive win in such a short space of time has a questionable logic to it in my opinion.
4. The tournament doesn't reflect the trainer's actually ability with Pokémon. One on one battles in an elimination style tournament essentially means it's a sudden death competition. Iris had such a advantage that effectively she won before the match had even started. If it had been two against two or three on three then the greater degree of diversity in Pokémon chosen and the requirement to beat more than one opponent would be a better way of determining a trainers ability to work with their Pokémon and adapt to different situations.
5. It continues the series trait of giving Pikachu a beating. Pikachu is Ash's closest and strongest partner and should be given a brighter spotlight than he was during the BW series. In my opinion the writers unfairly treated him like a punching bag. I accept that Pikachu is still brittle in his strength and had a massive type disadvantage here but it was still a bad loss that should not have happened. Why did he have to get slammed into the wall like that - that was hard to watch. And this comes on top of loosing to a Panpour in the first gym battle against Cress (when Oshawott beat a Pansage), nearly loosing to a Swanna in the battle against Skyla and going out to Cameron's Lucario in the end of the series. Poor Pikachu.
If they really wanted to give Ash such a bad loss why not demolish a different Pokémon. It would not have been as bad if Ash had lost with a different Pokémon. Oshawott would be my preferened candidate. He could have used palpitoad and lost given palpitoad's lack of experience. Even Snivy is another possibility given she would be a general disadvantage. But Pikachu has been with Ash since the beginning, he's Ash's most trusted and closest partner and the one he loves the most so it's not unreasonable that by this stage in Ash's career he should be able to hold his own a little better than this. The writers spent the series picking on him. I'm glad he's getting the spotlight he deserves in XY.
6. In any case it's a relatively hollow victory on Iris's part. As far as I can see she won because of a type advantage rather than her own skill. She didn't win that conclusively and she got lucky with the last focus blast. Pikachu put up a very good fight and probably nearly won. If he could have blocked or dodged that final focus blast he probably would have been able to score a winning blow with Iron tail - I don't know. Either way it's a shallow achievement on her part. She got lucky because the odds were in her favour yet still felt the need to call Ash a kid.
If the episode has a saving grace it's the hug scene between Ash and Pikachu after the battle which brings out their friendship and love for each other in as good a way as a victory would have and in some respects better than.