I'll repeat what I posted earlier, it's not Ash's fault that he has more cards in his hand than Leon. Maybe Leon's overconfident, maybe Leon believes it's not fair to limit Ash to having to use a single Trump Card, or maybe Leon wanted to fight Ash at his absolute peak. Regardless of which it ultimately is, I can't say it's really that unfair. Leon represents Galar to a fault, so Dynamax is the only thing he knows and cares about, which is fine. But Ash has gone on a Journey just about everywhere, yeah he's from Pallet Town, yeah he represents his second home the Alola region, but he's earned the ability to use Mega Evolution, the Z-move, and Dynamax, why limit him to a single choice exactly? Because Leon only has 1? Welcome to Shonen guys, the protagonist always needs a transformation or boost of sorts to beat the final boss.