James, Lana and Sophocles were the only questionable entries in the Top 8, and even then they at least bothered to show Lana and Sophocles training before the league (along with weaponising their non-battler skills they built up over the series).
My only huge problem is that Lana NEVER done an official battle before the league, which really feels like something mandatory. James got in through a kinda farcical battle with Jessie and inevitably got stomped, while Sophocles had a crash course with Kiawe, so there was inevitable serious business training involved there, as compressed as it was.
That leaves Hau, Gladion, Kiawe, Ash, and Guzma, who were all relatively seasoned battlers.