Given the fact that he ended up winning the Kalos League after blitzing through the 8 Gyms in a couple days, I’m sure that’s what the writers were going for but at a smaller scale. The entire Team Flare plot hinged on Alain’s collection of the Mega energy, his fight with Manon caused the group break up which led to Chespin getting used as a Zygarde battery, and betraying Ash led to Ash getting captured and the entire conflict atop Lumiose Tower. Alain literally caused everything bad that happened, and the climax of the show was 5 episodes of everyone fixing his mistakes, a sharp 180 from the rest of the show being mostly about Ash winning the Kalos League and battling Diantha. Greninja’s entire story arc was about it finding a trainer that can bring out its true potential so it could become the strongest, Ash-Greninja being an amalgamation of that, and it ended up having a jagged resolution because the writers chose to rather focus on Alain’s dream of being the strongest instead. The show quite literally revolved around Alain at that point. You would’ve thought he was the protagonist.
And if Alain had a life outside of battling, we never actually saw it. He was Sycamore’s assistant before his Mega journey but only ever saw them working together in that one flashback, and after that it was solely just battling and collecting mega energy. We know Leon likes to hang out with Pokémon on his downtime, especially if he gets lost, and we actually get to SEE that. We also know he takes time out to take care of Hop as well. Despite the fact that Alain had more screentime, Leon has a lot more to work with his character. And again, at least we got to see an instance of Leon training as opposed to just not ever with Alain.
And I think you’re mistaken because as of episode 115, we do know half of Leon’s team; Charizard, Dragapult, and Rillaboom.