Let’s look at the facts: Alain pre his training arc was already around E4 level, Siebold was just a bad match up. He even held his own against Steven. After his training arc, he could defeat 9 MEs in a row and defeated Malva without taking a break and defeated perfect AG, who, in a weaker state, cornered Diantha’s Mega Guardevoir. Thus, Alain at the end of XYZ is far stronger than E4 members and closer to champions than to E4 members.
Against Leon, he had the misfortune of real world problems affecting his battles: It was clear that Leon will win, and due to having only half an episode instead of an entire episode they had to rush the battle. Even then, he was skilled enough to counter Leon’s G-Max on the spot with a normal team member, and using Malamar against Charizard seemed like a good idea, too. This smart battling style was already shown in XYZ, when he used Sandstream to conceal Pikachu’s movements or the Bisharp strategy.
There’s no reason to assume he’s weaker than any of the champions not named Leon, and even less reason to assume a champion without feats is stronger than him. So it probably depends on small margins when he is up against the 5 remaining champions.