Comparing this tournament to the Wallace Cup really isn't fair and doesn't make that much sense.
The Wallace Cup was a chance to bring back May and showcase Wallace, a character who never appeared in AG, and also to show contests on a much larger scale than we'd seen before outdside of a Grand Festival. May was also the perfect choice to showcase Glaceon, who wound up being Dawn and Piplup's final opponent. Most importantly the cup was the apex of a long-running arc in which Dawn had twice failed to make it through the appeal round, even after trading for Aipom/Ambipom who seemed like a secret weapon at that time. That arc was designed to bring Dawn back out of her losing streak by giving her the most significant win they could; they didn't want her to defeat Zoey so early, so they brought back May to be her opponent and idol. People whinge because Dawn was a newbie but she was using her strong starter pokemon against a newly evolved pokemon who had only been born in the middle of the previous arc and was hardly May's strongest. A four-episode arc to bring back May just so she could steamroll everyone and win a ribbon we would NEVER see the benefit of because we'd never see her Johto Grand Festival... that would be fun but pointless. Giving the win to Dawn was absolutely right, and the Wallace Cup was a perfect culmination for a pretty dark period in Dawn's character arc (by this show's standards at least) in which she was very depressed and had considered quitting altogether. May was hardly useless, after all she made it to the final and knocked Zoey out of the competition. Unfortunately, everyone turned this well thought-out arc into a competition for who was the writers' favourite and tried to use May's experience as the sole excuse for her winning even though that doesn't hold up at all in this case. Piplup won the battle and Dawn finally gained back her self-esteem as well as winning a long-awaited second ribbon. That's all there is to it.
This World Tournament, and obviously we don't know everything to expect just yet, isn't the same deal. The prize is apparently a chance to battle Alder. That's a big deal for anybody but it's not a crucial stepping stone like a badge or a ribbon is, taking you a percentage closer to the regional competition. After this arc, we won't have a tangible item which makes the winner any more qualified. No matter who wins, Ash still goes to the Unova League. That's not a problem, because there should be character development aplenty and some really cool battles. It doesn't immediately affect the progression of the template-based story arc, so the important thing in this battle will be which character logically should win. Two crucial things to consider;
1. Dawn has returned for a reason. May came back partly to showcase a bunch of evolutions on her team and to update us on her progress, and in the Wallace Cup she defeated Zoey which a talented coordinator needed to do. Most importantly she was the worthy opponent Dawn had to defeat in order to believe in herself again. Dawn was chosen to come back at this specific point for a reason. It might purely be "hey, let's bring that popular character back after more than a year away" but they could have chosen somebody else. She's the most logical choice for Cynthia to bring along though- they kinda saved the world together that one time.
2. This Iris arc in this tournament revolves around her specific relationship with a single pokemon. We know she'll defeat Georgia, her rival, using Dragonite. This is a huge step for her. However, Dragonite will then have to battle Mamoswine, Dawn's most battle-orientated pokemon and one of few which can physically rival a behemoth like Dragonite, not to mention having a type advantage and having been trained extensively from being a disobedient pokemon in the past.
It is clear that Dawn was brought back primarily to be a worthy opponent for Iris in this major character development arc (as May was to Dawn before, and there's no shame in that) and which of the two wins will vary based on a few factors; whichever of them wins this round will subsequently be in the Top 4 for the Junior Cup. This makes it possible that one of them will go on to battle Ash or Trip, both of whom are guaranteed a place in the final as far as I can tell, or possibly Cilan or Burgundy. And if either of them battles Ash or Trip, I think it unlikely that they would win because as much as Iris is being developed in this Dragonite plot I can't see her eclipsing Ash in a tournament like this or being the one who gets an official battle against Alder. Like, can you imagine if Brock had battled Palmer instead of Ash? I fully expect the final of this tournament to be between Ash and Trip, so one of the two will knock the winner of this battle out in the next round. I can see Iris battling and losing to Trip or Ash, while Dawn will probably battle against Ash if she wins.
I could be entirely wrong.
But the stuff I said earlier about comparing this to the Wallace Cup, that stuff's legit. No bollocks there.