>>39812145I keep bringing this up, but Kukui designed this league for accessibility and bringing the people of Alola together, not to accurately judge the battling and competitive ability of trainers. Kukui didn't lock the league's access behind a skill-based requirement such as clearing trials or getting a certain number of badges. Anybody could participate. That's why people who have no business being in a league such as all of Ash's friends and Team Rocket were part of it.
To add insult to injury, the preliminary round (which usually is a test of skill) in this league was a battle royal, not an actual battle. The goal was to survive until you got to the top 16, and you didn't even have to battle to get to the final tournament. (James certainly didn't.) People who actively did battle such as Plumeria were actually eliminated. And this type of competitive format prioritized teamwork, so people with strong friendships or alliances could easy clear through the tournament. Also, avoiding powerful trainers was also important.
And for your list, Ilima was actually the top favorite to win the tournament, and he was an experienced battler with Mega Evolution. He only lost because Guzma capitalized on Mega Kangaskhan's weakness. If Ilima used any other Mega in this fight, he would have probably won.
>>39812189Hau had a lot of potential, as his Decidueye was extremely powerful and nearly wiped Rowlet out if it weren't for bullshit plot. Hau trained Decidueye on how to time its reactions and moves so that they had the best effect. His Alolan Raichu also took out quite a number of powerful foes as well.
Hau was certainly among the more powerful trainers in the tournament. He is probably at Kiawe's level if not higher.