The problem is that he's only at E4 level when the writing staff want him to be. And sure he beat Iris who's a champion now but if Ash had to face someone like Cynthia right now with the same team that he beat Iris with I bet he wouldn't beat Cynthia.
tbh, Journeys doesn't count yet, especially if we look at the showings of the Pokemon. The only Pokemon currently at Champion level are Dragonite and Pikachu, with Dracovish following and after that we get Lucario and Sirfetch'd, who are followed by Gengar. Considering we hardly see them battle, we can only judge them on the battles they had so far. And while Rinto and Bea have been strong, they are not nearly as powerful as E4 members or Champions. Same goes for Vizquez. You can say Korrina is low E4/8 gym leader level, but considering Gengar still got thrashed by her Mienshao, Gengar drags the team down. So the only true indication we have so far is Iris. Despite Dracovish taking down her Dragonite, it faced Ash's Dragonite beforehand, so that isn't any indication either, despite it going toe-to-toe with Charizard, because it got powered-down in Journeys in favor of Haxorus.