Ash is doing really good right now, well if we are ignoring the Goodra-Stuff.
HIs competence definetly rivals his Sinnoh one, and we knew what the writers had to pull there to make him lose.
So i wouldn't call people who think he can defeat the E4 delusional. It's going to be exciting for sure though.
Here's the thing, we've already seen what happens to Ash when he goes up against an Elite 4 member at his most competent, he's gets absolutely annihilated like he did against Flint, it wasn't even a contest, Infernape just wiped his Pokemon. Tobias was a joke opponent compared to Flint, Ash actually did something against him.
For Ash to get anywhere near the Elite Four, he's going to need a hell of a lot more than his Sinnoh competency, a hell of a lot more, Elite 4 members have been training for years and are far more experienced, far more skilled and far more competent than Ash is. The problem is the only way we will ever see Ash make the sort of progress he needs to be able to actually take on the Elite Four is if he ages, but nope, he's going to be a kid forever.
Anyway, we're getting ahead of ourselves since Ash actually hasn't even won any league yet, and we all know that he's going to lose to someone like Alan, and the salt from show watchers, including myself, will be glorious.
Well Ash did made a promise to Diantha...
Ash makes the exact same promises every new region and always comes up short, hell, we've been waiting nearly 20 years for him to fulfil his promise to win a league.