Considering no notable characters have a full team, my only guess is that the Alola League is going to have rules different from other Leagues, considering Ash will likely stick to just using his regional captures again. Battles are probably all going to be 3 vs 3 at the most.
I’m likely guessing it’ll be just 1 vs 1, just because all the classmates only have 1-2 Pokémon each.
That is making the assumption that all of Ash's classmates will participate in the league which is not a safe assumption to make, the only one of Ash's classmates that it safe to say that is participate in the Alolan League is Kiawe who has specifically express interest in joining the league. Also as of right now the only characters that either confirmed or implied to be in the league is Ash, Kiawe, Hau, Gladion, and the Royal Masked and outside of that any other character is just pure speculation.
I know some people here seem to like to jump to conclusions that league won't have any full battles but there isn't really anything to suggest that, and before you try to argue that none of those characters don't have full teams it's important to note that it's not that unusual to not see a rivals full team for the battle, as all of those characters can easily just show up at the league with a full team.
Also provided Ash even faces all of his rivals at the league instead of having some of the rivals eliminate each other then chances are that Ash's battle against Ilima and Kiawe will be a 3vs3 so it won't be an issue that we don't see their other 3 pokemon and Ash's battle against Hau, and Gladion can easily be a full battle with them both easily getting pokemon that we may more may not see before the league, as for the Masked Royal either Ash's battle with him will be a full battle if it's actual league match or if the battle winds up being a reward for winning the Alolan League it could possibly be a 1vs1, even in the case of a full battle the Masked Royal could easily show up with a full team.
As for Ash he could easily get Meltan, and considering the writers Poipole could easily return, or Ash winds up catching another pokemon even though a lot of people would hate that option or he could just use a reserve.
Look I get that Sun and Moon might not have been having as many battles as some people would like but can people stop just trying to jump to conclusions, right now there isn't any reason to think that the Alolan league won't have full battles and really saying it is some how likely league is somehow going to lack full battles even though Kukui is basing the Alolan league on the other main regions leagues and those leagues had full battles, is really just jumping to conclusions.
Look unless it's specifically stated otherwise then chances are there are going to be full battles at the league.
