For real though
Leon has Charizard because he's meant to be a stand in for the older players. This is why they stress he became a champion at 10. He's your senpai, who passes on the mantle to you after you beat him. His ace is still Gen 8 in a sense because Gmax is Gen 8, like Diantha. And thankfully, Galar didn't get cucked out of getting its own gmaxes like Kalos did with megas.
Though, ideally, Leon would just have the Kanto starter that's strong against your Galar starter and gmax blast/venu would be in the base game from the get go, but this is GF we're talking about. SWSH has many questionable or outright dogshit design elements but this is fine in a sense, just not done ideally.
